Fair Use is but one of the limitations and exceptions outlined in the Copyright Law, but it is probably one of the most important. Fair Use is defined in Section 107 of the US Copyright Law, the full text of which has been copied here:
§ 107. Limitations on exclusive rights: Fair useNotwithstanding the provisions of sections 106 and;106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include (1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;(2) the nature of the copyrighted work;(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and(4) the effect of the use upon the potential market for or value of the copyrighted work.The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
The preamble lists some examples of uses typically covered as fair use ("criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research,"). This list is neither complete nor exclusive. Keep in mind fair use is a flexible ad hoc rule, and there is no exhaustive list of fair uses. Rather than create a list, the fair use statute contains four minimum factors to consider.