Proprietary license

A proprietary license can be simply defined as a list of everything the law allows but the copyright holder does not.

Use of this tag is likely to change in the future.
Most platforms are dominated by commercial games using a proprietary license. However, there are some platforms where proprietary games are in the minority or opposite from the original platform ecosystem, such as *NIX based systems (Linux, GP2X, Pandora, OS/2, and others). Primarily this tag is intended to distinguish proprietary games among platforms that tend to lack them.
Also, the game art form, while initially founded on non-proprietary games, at some point came to be overwhelmingly dominated by proprietary games. This is likely to persist for some time. But eventually, non-proprietary games will again be the norm. At that time this tag should become relevant for all proprietary games.

Note also that proprietary and non-proprietary licenses do necessarily require commercial sales activities or not.

Finally, under current US law, international treaty, and law of many other nations, not specifying copyright terms in precise detail means the work is licensed according to the copyright terms for the jurisdiction in which it was created and/or published. Therefore, no license, or an imprecise license is by default, proprietary. Under current US law, works that were released without restrictions as intended by the author have retroactively become restricted even in cases where the author is deceased or the author is unknown. Sadly, many early games of the game art form were not been precisely licensed and any that have remained this way are legally defined as proprietary.