What is Client Access License?
A client access license (CAL) is a type of license that binds the licensee to a set of user terms that limit the use of the organization's services. This is usually done using software that is accompanied by a certificate of authenticity and a multi-digit license key. The end user must verify their CAL by entering the license key numbers in a specific field before downloading the software.
Microsoft is just a company that uses CALs to ensure the proper use of its systems and applications. Whether multiple CALs are required or not, or individual CALs are used, depends primarily on whether a product is used for personal or business purposes. For business purposes, CALs can be assigned to multiple people, but multiple users cannot use the software at the same time. Larger organizations generally benefit from device CALs that can be applied to any device or computer connected to a shared server.