Refers to any computer software that has restrictions on any combination of the usage, modification, copying or distributing modified versions of the software. Proprietary software usually can be distributed at no cost or for a fee. Proprietary software may also be called closed-source software.
See "Is Software Ownership the Same as Licensing?" in the in the "Did You Know..." section of Webopedia.
Also see "All About Software: Categories of applications software explained" in the "Did You Know..." section of Webopedia.