Closed Source

The extreme end of ProprietarySource, where you don't get a chance to look at anything resembling the source code.

E.g. commercial software, shareware and freeware that's only "free as in beer" and not also "free as in air". (Microsoft InternetExplorer, for instance.)

There is OpenSource software, and there is non-OpenSource software. Some non-OpenSource software has source available, but under a license that doesn't qualify as OpenSource. And some non-Opensource software has no source available to you at all. That is ClosedSource software.

The licensing terms of ClosedSource software varies. Typically, the user has the right to run the program, usually with restrictions on the number of copies, on what machines it can be run, and who can run it.

The user is often prohibited from looking under the hood, trying to disassemble the program, or trying to change it.

See also ProprietarySource.