Fair use

Overview
Fair use is a doctrine which establishes the right to copy works, or portions thereof, which it would not normally be considered legal to copy, for specific types of use, including:
 * educational use
 * criticism or commentary
 * other "transformative" uses

Reference

 * Bloggers' FAQ - Intellectual Property by the Electronic Frontier Foundation
 * Bloggers' FAQ - Intellectual Property by the Electronic Frontier Foundation