I get a lot of questions about licensing which seem easy to me. I've just realized that the cause is probably that people don't understand all the pieces of the Free Software licensing system. I say "system" because the GPL really is like a piece of software that runs on top of LegalOS XP (home edition). Even though there are many legal systems in the world, most countries have agreed to the Berne Convention. So, copyright laws are quite similar around the world.
So, here's a primer:
Copyright law grants to copyright holders some exclusive rights.
a. These rights include copying, modification (what copyright law calls "preparing a derivative work"), and redistribution.
b. If you write software, you're probably the copyright holder, unless you are at the time working for some company as an employee. You don't have to do anything special to obtain a copyright. As soon as you save the document, pixies sneak into your computer and deposit the copyrights directly onto the document. But it's still a good idea to use copyright notices.
Exclusive means that the copyright holder gets to decide who can exercise these rights.
a. In order to let someone else exercise these rights, the copyright holder issues a license.
If someone exercises the rights outside the terms of the license, they're infringing the copyright.
a. We speak of these as "license violations".
b. Because the copyright holder is the only one whose legal rights have been infringed, they're the only one who can enforce the license.
Sometimes, a copyright holder wants something very close to, but not exactly, standard terms. In this case, they can issue an exception to the license permitting this. That's effectively a modification of the license which makes it strictly more permissive.
The copyright holder can do this because of (2) above.
There are at two common cases of this:
a. The standard terms don't permit linking to a library which the copyright holder wants to permit linking to. FSF has written exceptions for this case.
b. Someone has convinced the copyright holder that they should be treated specially and have rights above the standard terms. Perhaps this is because they have paid the copyright holder. Because the terms for this can vary wildly, and can sometimes support proprietary software, FSF doesn't have standard text for this.
You can also assign your copyright. By way of analogy, licensing software to someone is like inviting them to visit your house; assigning copyright to someone is like selling them your house.
a. You might want to assign your copyright to someone else if they promise to do the work of enforcing the license, or they otherwise won't take your patches.
We maintain a list of free software licenses. A license gets on this list by consensus of our licensing committee. But the committee isn't a bunch of alchemists. They don't even have pointy hats. They just look at the terms of the licenses. Decisions are made based on the Free Software Definition.Usually, you can tell if a license is a Free Software license by matching its terms to other licenses in the license list. This is not to say that a license which consists only of terms from other Free licenses is ncessarily a free license. For example, if I took only section 11 of the GPL and called it my license, it would (a) not be a license and (b) not be free. But a license that differs from another only in the name of sponsoring organization will be judged the same.
We encourage the use of standard licensing terms.
a. Writing a new license, rather than using an existing standard license, is a bad idea because it increases the burden on people who want to re-use your software. They have to understand some new set of terms. And then they ask me to tell them if it's a free software license.