Open source license
Any document that attempts to specify open source usage and distribution of software. These licenses are usually drafted by experts and are likely to be more legally sound than one a programmer could write. However, loopholes do exist.
Here is a non-exhaustive list of open source licenses:
1. Public Domain - No license.
2. BSD License - An early open source license
3. General Public License (GPL) - The copyleft license of the Free Software Foundation. Used for GNU software and much of Linux.
4. Artistic License Less restrictive than the GPL, permitted by Perl in addition to the GPL.
5. Mozilla Public Licenses. (MPL, MozPL) and Netscape Public License (NPL).