Open Software License: Meaning (information, definition, explanation, facts)

The Open Software License ("OSL") is a software licence created by Lawrence Rosen; the Open Source Initiative (OSI) has certified it as an open source license.

The OSL is, in the main, a fairly standard copyleft license. It's main peculiarity (and the reason it was written) is its patent termination clause:

10) Mutual Termination for Patent Action. This License shall terminate automatically and You may no longer exercise any of the rights granted to You by this License if You file a lawsuit in any court alleging that any OSI Certified open source software that is licensed under any license containing this "Mutual Termination for Patent Action" clause infringes any patent claims that are essential to use that software.

Many people in the free software / open source community feel that software patents are harmful to software, and are particularly harmful to open source software. The OSL attempts to counteract that, by creating a pool of software which a user can use if that user doesn't harm attack of it with a patent lawsuit. So the OSL can be thought of as an offer to pay patent holders not to use patents to harm open source software, "you can use any OSL-licensed software, provised you don't sue any of it for violation of patents"; if a patent holder doen't think this is a fair offer, they are entirely free to decline it, and are no worse off.