With proprietary software usually is a change - as opposed to free software - not allowed, which is why it is colloquially referred to as non-free software. Their proliferation is - depending on the license agreement, such as in freeware or shareware - but partially allowed.
There are three ways to protect proprietary software: software patents, copyright, and / or by the treatment of the source code as a trade secret (English closed source ). The practice to keep the source code of computer programs under wraps, came on in the late 1970s or early 1980s. The company Microsoft is considered a pioneer of the proprietary development and distribution model for software.
The FSF defines proprietary software such that they, in contrast to free software or public domain software may not be adapted and used as desired by a third party. (And also "free software " is often not everything is allowed: for example software, which is under a copyleft license, the freedom has to third parties except for a software to make proprietary, what is possible in public domain or under permissive licenses, sometimes there are the requirements Attribution of the original authors, etc )
Others see as a core feature of proprietary software, the non-availability of the source code, the object model would then open source software ( Open Source English ).
For software whose source code is available, and not any for some, but, use cases, the re-use allowed ( semi- free software ), there is controversy about their classification. Example of such software would be Photoshop 1.0.1 whose source code was published in 2013 under a license which, although any private use allowed, but a commercial re-use and redistribution excludes.
Even proprietary software should not be equated with commercial software. Commercial software that is sold or licensed to customers, both proprietary and free software ( usually combined with service offerings ) be; the difference is, that may be the case of proprietary software resale and adaptation is restricted or prohibited. Free proprietary software is called freeware.
The adjective can be applied to proprietary protocols ( eg for networks ) and file formats.