[1][2][3][4] Commercial apps are licensed to end users or businesses: in a legally binding agreement between the proprietor of the software (the "licensor") and the end user or business (the "licensee"), the licensor gives permission to the licensee to use the app under certain limitations, which are set forth in the license agreement.
In the case of Microsoft, the consumer retail or "off-the-shelf" products generally use very similar licence agreements, allowing the licensee to use the software on one computer, subject to the usual terms and conditions.
For businesses, Microsoft offers several types of licensing schemes for a range of their products, which are designed to be cost effective, flexible, or both.
A CAL legally permits client computers to connect to commercial server software.
Microsoft Server products require a CAL for each unique client regardless of how many will be connecting at any single point in time.
Microsoft SQL Server can be licensed for CALs, or alternatively by CPU cores.
Terminal Services is a function of Microsoft Windows that allows several types of connections to the server components of the system.
[9] The system for enforcing the number of TS CALs ("Microsoft Enforced Licensing") used on versions later than NT was abused by the "FLAME" malware, leading to a patch in 2012 restricting the Certificate Creation system used for Terminal Services.