What are compatible licenses, and what does GPL compatible mean?
In order for two licenses to be compatible it must be possible to mingle code under both licenses in a new work. When this is done the result is that the terms of both licenses must be met for the work as a whole. The GPL makes this feature of copyright law explicit by stating that if you cannot for any reason (e.g., because of another license) meet the terms of the GPL, the GPL grants no rights at all. In order for a license to be GPL compatible, then, you must be able to meet both the terms of the GPL and the other license simultaneously.
