A CAL is a license that enables a user to use the server’s services; it is not a piece of software. A Management License (ML) may also be necessary for the device being controlled if you manage the devices on your network using management software like Microsoft System Center.
What do you mean by client access license?
In a legally binding agreement between the owner of the software (the “Licensor”) and the end user or business (the “licensee”), the licensor grants the licensee permission to use the app subject to the conditions set forth in the license agreement.
Commercial apps are licensed to end users or businesses.
The consumer retail or “off-the-shelf” products from Microsoft typically employ relatively identical license agreements, allowing the licensee to use the program on one computer while adhering to the standard terms and conditions.
However, Microsoft provides a variety of license plans for organizations that are intended to be affordable, flexible, or both for a number of their products. Licenses are necessary for commercial server software like Windows Server 2003 and SQL Server 2005.