Closed source software

Closed source software is any type of software which is placed under a non-free license agreement. By non-free, we do not mean that the software is not free of charge, but that it is bound by proprietary license restrictions that contradict the open source definition. Examples of closed source software include Microsoft Windows and Adobe Photoshop.

In spite of the appearance of the terminology, some closed source developers provide the source code to their work. Examples of this include Microsoft's shared source initiative and the OpenGL Utility Kit (GLUT).