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 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 however, Microsoft offers several types of licensing schemes for a range of their products, which are designed to be cost effective, flexible, or both.
Commercial server software, such as Windows Server 2003 and SQL Server 2005 require licenses that are more expensive than those which are purchased for desktop software like Windows Vista. All clients that connect to these server products must have a license to connect in order to use their services. These special purpose licenses come in the form of a CAL.