Linux and most of the software associated with it are released under the GNU Organization's General Public License (GPL). The GPL protects the rights of software users and developers, but it also holds them to certain responsibilties.

Rights:

• Users have the right to copy, edit, and freely distribute software.
• Users have the right to the source code.
• For developers, any patent made on the software must be licensed for the public's free usage.

Responsibilites:

• Users and Developers must give the same GPL rights given to them if they distribute the software.
• Users and Developers must make it known that these GPL rights are given.

Visit the GNU website for the actual wording of the GPL and lots more details.