The Creative Commons- Flikr

Attribution License- You give anyone the permission to use your work, as long as they give you credit for it.

Noncommercial- You give anyone the permission to use your work, but for noncommercial use only (so they can't make a profit off of your work).

No Derivative Works- You give them permission to use your work, but they can only copy it word-for-word. They can't paraphrase your writings, or change it just a little bit so it isn't exactly yours.

Share Alike- You let others share derivative forms of your work (pretty much the same, but only a small change) but ONLY if they have the same license as you do.