proprietary software is software whose copyright owner does not permit others to distribute further copies. Proprietary software almost never includes source code, as this would allow anyone to remove identifying text or images from the software, or even reverse-engineer and rewrite it from the ground up, recompile the code, and distribute the resulting software as their own. (In the case of reverse-engineering, such redistribution could arguably be legal, as ideas are not supposed to be copyrightable or patentable, although in practice copyrights and patents are often granted for such; see Issuepedia:Intellectual Property.) This generally means that only the copyright owner can provide complete support for the software, as nobody else has access to knowledge of the software's inner workings.
It is essentially the opposite of free, open-source software.
- 2006-08-28 Why proprietary software is dangerous for business-critical applications by Robin 'Roblimo' Miller