Fair use basically permits that certain uses of copyright-protected works do not require permission from the copyright holder. Four factors are used to determine if a use is fair:
Faculty may make limited use of another author's work without asking permission under the "fair use" educational provision of copyright law. However, since copyright can be a grey area, faculty are encouraged to use the Fair Use Evaluator to better determine "fair use" for different situations.
Specific guidelines for legally using various medium can be located at Fair Use Guidelines for Teachers