Software license terms: glossary from CAL to LTSC

What do the terms around software licenses mean? A license is the right to use a piece of software. The product key is the code you activate it with. On top of that come terms for the type of license (retail, OEM, CAL, core), for the release of the software (edition, version, LTSC, SE) and for the supply of updates (mainstream support, extended support, ESU). This glossary explains 53 terms in a few sentences and names, for each one, the guide that covers the topic in depth.

Quick decision

Which terms you need depends on what you are buying:

You are buying …	Terms you should know
Windows for a PC	Edition, version, product key, activation, digital license, retail, OEM
Office	One-time purchase, subscription, Microsoft account, Office LTSC, 32-bit and 64-bit
Windows Server	Core, core pack, Standard, Datacenter, OSE, CAL, user CAL, device CAL, RDS CAL
SQL Server	Per core, server + CAL, Express, multiplexing
Software for a fixed-purpose device	LTSC, IoT Enterprise, feature update
An earlier version	Lifecycle, mainstream support, extended support, end of support, ESU

All support dates with day, month and year are in the
Microsoft end of support calendar.

Terms from A to Z

0–9

32-bit and 64-bit. Two builds of the same program. Office is available in both. For Office LTSC 2024, Microsoft recommends the 64-bit version on devices with at least 4 GB of memory, but advises checking compatibility with existing add-ins first. More on this:
Office 32-bit or 64-bit.

A

Activation. The technical process that links the product key or the digital license to the device’s hardware. In doing so, Microsoft checks whether the license matches this device. In Windows 11 you enter the key under Settings → System → Activation. Step by step:
Activate Windows 11.

C

CAL (client access license). A client access license. According to Microsoft, it is not software but the right of a user or device to use a server’s services. You need CALs in addition to the server license. Exactly when is explained in
Windows Server CAL.

CAL Suite. A bundle of several CALs in one license. Microsoft offers the Core CAL Suite and the more extensive Enterprise CAL Suite. A suite is assigned to one user or one device and cannot be split across several. Context:
Windows Server CAL.

Click-to-Run. The installation technology of current Office versions. It has replaced the earlier Windows Installer (MSI); Microsoft calls this the biggest difference between Office 2016 and Office LTSC 2024. The installation is shown in
Install Office Professional Plus.

COA (Certificate of Authenticity). A label of authenticity on the device. On a new PC with Windows, according to Microsoft, the product key is stored in the device, included in the packaging or printed on this label. More under
Retail or OEM.

Core. A processor core. Windows Server Standard and Datacenter are licensed by the physical cores of the server: at least 8 core licenses per processor and at least 16 per server. The calculation:
Licensing Windows Server.

Core pack. The sales unit for core licenses. According to Microsoft, Windows Server is available as a 2-core pack and as a 16-core pack, SQL Server in 2-core packs. What that means for your requirements is under
Windows Server license: costs.

D

Datacenter. The large edition of Windows Server. According to Microsoft, it allows an unlimited number of virtual machines on a fully licensed server. The comparison:
Windows Server 2025 Standard or Datacenter.

Device CAL. A client access license per device, no matter how many people work on it. It fits when several people share one device, for example in shift work. Weighing it up:
User CAL or device CAL.

Digital license. A method of activating Windows without entering a product key. According to Microsoft, it is created, for example, with a free upgrade or a purchase in the Microsoft Store app; with a purchase from the Microsoft Store online you receive a product key. If it is linked to a Microsoft account, that helps after a hardware replacement. More:
Activate Windows 11.

Downgrade rights. The right to use an earlier version instead of the one purchased. The Windows 11 license terms grant it for devices that were delivered with a Pro version preinstalled, and only for as long as Microsoft still supports the earlier version. Details:
Retail or OEM.

E

Edition. The feature tier of a product, for example Windows 11 Home, Pro or Pro for Workstations. A product key only ever fits its own edition. Overview:
Windows 11 editions.

End of support. The day after which Microsoft no longer delivers security updates. Overviews:
Windows Server end of support and
Office end of support.

Essentials. An edition of Windows Server with limits of its own. According to Microsoft, it generally needs no CALs. Limits and use:
Windows Server 2025 Essentials.

ESU (Extended Security Updates). A paid Microsoft program for individual products after the end of support. It delivers security updates for at most three more years, but no new features and no technical support. Microsoft calls it a bridge. Example:
Windows 10 end of support.

Express. The free edition of SQL Server with fixed upper limits, for example for the size of a database. When it is enough is shown in
SQL Server Express: limits.

Extended support. The second phase under the Fixed Lifecycle Policy. Microsoft continues to deliver security updates but no longer accepts requests for new features or other fixes. Not every product has this phase. All dates:
End of support calendar.

External Connector. A license that allows any number of external users to access a server, for example customers or suppliers. It is an alternative to individual CALs for these people. Context: Windows Server CAL.

F

Feature update and quality update. A feature update brings new features and a new version number; a quality update fixes bugs and security vulnerabilities. LTSC releases receive only the monthly quality updates. More:
Windows 11 LTSC 2024.

Fixed Lifecycle Policy. Microsoft’s set of rules with fixed dates from release: at least five years of mainstream support, followed by extended support for some products. It applies, for example, to Windows Server and SQL Server. Dates:
End of support calendar.

H

Hardware change. If you replace essential parts such as the motherboard, Windows, according to Microsoft, no longer finds a license that matches the device and has to be reactivated. The Activation troubleshooter helps with this. Procedure:
Transfer a Windows license to a new PC.

Hyper-V. Microsoft’s virtualization technology. It lets several virtual machines run on one device. Hyper-V is included in Windows Server and in Windows 11 Pro, Enterprise and Education. What that means for licenses:
Windows Server and virtualization.

I

Installation media. A USB flash drive or a DVD from which you reinstall Windows. Microsoft provides the Media Creation Tool for this; the flash drive needs at least 8 GB and is erased in the process. Instructions:
Install Windows from a USB flash drive.

IoT Enterprise. A separate Windows product line with lifecycle entries of its own. According to Microsoft, the IoT Enterprise LTSC releases receive updates for longer than the Enterprise LTSC releases of the same year – for the 2024 release until October 10, 2034 instead of October 9, 2029. More:
Windows IoT Enterprise LTSC.

ISO file. An image of installation media in a single file. It is used to burn a DVD, create a USB flash drive or install a virtual machine. Instructions:
Create a USB flash drive from an ISO file.

L

License. The right to use a piece of software. It is not the same as the product key: the key is the technical means of activation, the license is the right of use behind it. Which types exist:
Retail or OEM.

License terms. The publisher’s contract text that you agree to during installation or activation. Among other things, it governs transfer, support and downgrade. For Windows 11, according to the license terms themselves, it can be found at aka.ms/useterms and in Windows under Settings → System → About. The most important points:
Retail or OEM.

Lifecycle. The period during which Microsoft supplies a product with updates. Microsoft publishes it for each product on a separate lifecycle page. All dates:
End of support calendar.

LTSC (Long-Term Servicing Channel). A release of Windows Enterprise that keeps the same feature set for years and receives only quality updates. Microsoft intends it for devices with a fixed purpose, not for most office PCs. More:
Windows 11 LTSC 2024.

M

Mainstream support. The first phase under the Fixed Lifecycle Policy, at least five years. Microsoft delivers security updates and other fixes and accepts change requests. Dates:
End of support calendar.

Microsoft 365. Microsoft’s subscription for the Office programs. It includes new features on an ongoing basis and cloud storage and can be used on several devices. Comparison:
Office 2024 or Microsoft 365.

Microsoft account. The user account with Microsoft. With Office for home users, you redeem the product key once with this account and afterwards install from the account without entering the key again. So remember which account you used. Instructions:
Install Office with a Microsoft account.

Modern Lifecycle Policy. Microsoft’s set of rules for continuously updated products. A product stays supported as long as you keep it up to date. If there is no successor, Microsoft announces the end at least 12 months in advance. It applies, for example, to Windows 11 and Office 2024. Dates: End of support calendar.

Multiplexing. Technology that pools access, for example a web application in front of a database. According to Microsoft, this does not reduce the number of CALs required: every user and every device at the end of the chain counts. Consequences for SQL Server:
Licensing SQL Server.

O

OEM (Original Equipment Manufacturer). The device manufacturer. In everyday use, this is the name for licenses that are delivered preinstalled with a device. The Windows 11 license terms call this “software preinstalled on a device” and attach separate rules for transfer and support to it. According to Microsoft, the transfer rules do not apply to software acquired in Germany; there, Microsoft refers to the applicable law. More:
Retail or OEM.

Office LTSC. The Office release for environments that cannot install feature updates. Office LTSC 2024 receives five years of mainstream support and no extended support afterwards; no new features are added after release. More:
Office LTSC 2024.

One-time purchase. You pay once and use the software without an ongoing fee. Office 2024 is a one-time purchase for one PC or Mac. Security updates are included; new features and the move to the next major version are not. More:
Buy Office once instead of subscribing.

OSE and virtual machine. OSE stands for operating system environment, a running instance of the operating system, physical or as a virtual machine. Windows Server Standard allows up to two OSEs each time the server is fully licensed. Sample calculations:
Windows Server and virtualization.

P

Per core. A licensing model based on processor cores, without CALs. For SQL Server you need at least four core licenses per physical processor. When this pays off:
Licensing SQL Server.

Product key. A 25-character code in five blocks with which you activate Windows or Office. Keep it safe. This is how you find it again:
Find your Windows key.

R

RDS CAL. The client access license for Remote Desktop Services. Every user and every device that connects to a session host needs one. It is available per user and per device, and it must match the version of the server or be newer. More:
RDS CAL.

Retail. A license acquired on its own, not delivered with a device. It covers one device. The Windows 11 license terms speak of “stand-alone software” and allow you to transfer it to another device that belongs to you; for software acquired in Germany, Microsoft refers to the applicable law. More:
Retail or OEM.

Retirement date. The date on which Microsoft ends support for a product under the Modern Lifecycle Policy. It corresponds to the end of support. Dates:
End of support calendar.

S

SE (Subscription Edition). The name of the continuously updated server releases, for example Exchange Server SE and SharePoint Server SE. They follow the Modern Lifecycle Policy; Microsoft has not stated an end date so far. More: Exchange Server SE and SharePoint Server SE.

Server + CAL. A licensing model consisting of one license per server and one CAL per user or device. For SQL Server it is available for the Standard edition only. Weighing it up:
Licensing SQL Server.

Service pack and cumulative update. A service pack combines many fixes in one package. For SQL Server there have been no service packs since version 2017; Microsoft recommends the latest cumulative update there. More:
SQL Server end of support.

Software Assurance. An add-on program from Microsoft for a license. Among other things, it includes the right to new versions. Individual rights require Software Assurance or subscription licenses, for example licensing Windows Server per virtual machine. Where that matters:
Windows Server and virtualization.

Stacking. Licensing the same server several times with Windows Server Standard in order to run more than two virtual machines. Each additional full licensing of all cores allows two more. Sample calculations:
Windows Server and virtualization.

Standard. For Windows Server, the edition for servers with few virtual machines; for SQL Server, the middle edition between Express and Enterprise. Comparisons:
Windows Server 2025 Standard or Datacenter and SQL Server 2025 editions.

Subscription. You pay continuously for as long as you use the software. Microsoft 365 is a subscription: the programs receive new features on an ongoing basis, and you can use them on several devices. The comparison with a one-time purchase is in
Buy software once or subscribe.

U

User CAL. A client access license per person, no matter how many devices they access from. It fits when staff work with several devices. Weighing it up:
User CAL or device CAL.

V

Version. The development state of a product, for example Office 2021 or Office 2024, and for Windows 11 also 24H2 or 25H2. The version determines the end of support, the edition the feature set. Example: Office 2024 or Office 2021.

Typical cases

You are reading a quote for a server. It usually says “16 Core”, “Standard” and “5 User CAL”. That means: a license for 16 processor cores in the Standard edition and client access licenses for five people. Whether that is enough is worked out by the
license calculator.

You are comparing two Office offers. Pay attention to the version (2021 or 2024), the edition (Home, Home & Business, Professional Plus) and whether it is a one-time purchase or a subscription.

You are buying Windows for an existing PC. What matters is the edition (Home or Pro) and the type of activation. Both are stated on the product page.

At VivaKeys

Every product page states the version, edition, platform, license type and type of activation. You can find all products under Software and
Business. If a term in an offer is unclear,
ask us before you order.

Further guides from this topic block:

Frequently asked questions

What do you need a Windows Server CAL for? For access to the server. The server license covers the operating system, the CAL the right of a user or device to use its services. According to Microsoft, you need CALs for everyone who accesses it directly or indirectly.

What is the difference between a user CAL and an RDS CAL? The user CAL allows one person to access the Windows Server. You need the RDS CAL in addition if this person works on a session host through Remote Desktop Services.

Is a product key the same as a license? No. The license is the right of use, the product key the code for activation. According to the Windows 11 license terms, you may only use the software if you are properly licensed and it has been activated with a genuine product key or by another authorized method.

What does LTSC mean for Office 2024? Office LTSC 2024 is the release without feature updates. It receives five years of mainstream support until October 9, 2029 and no extended support afterwards.

What does “end of life” mean for Windows Server? It refers to the end of support: the day after which no more security updates arrive. For Windows Server 2025 that is November 14, 2034.

Sources

Checked on 2026-11-10 against the publisher’s information:

License glossary: CAL, core, LTSC, SE and other terms explained