A tenet of U.S. copyright law that describes the circumstances under which one can sometimes make use of protected works without first getting permission or paying the rights holder.
Fair use is a tenet of U.S. copyright law, found in 17 U.S.C. section 107. It is often referred to as a “safety valve” for free speech, and is one of the two aspects of U.S. copyright law that help to prevent copyright’s monopoly from interfering with freedom of speech, another important U.S. right enshrined in the U.S. Constitution. (The other aspect of U.S. copyright law that seeks to balance the copyright monopoly against the public's interest in free speech is the idea/expression dichotomy.)
Fair use is a set of guidelines, rather than a rule, and is evaluated on a case-by-case basis according to four non-exclusive factors. These are:
The purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
The nature of the copyrighted work;
The amount and substantiality of the portion used in relation to the copyrighted work as a whole;
The effect of the use upon the potential market for, or value of, the copyrighted work .
Because of its status as a "safety valve" for speech, fair use is often called upon or relied on by content users attempting to assert their rights under copyright law. However, because fair use is not clearly defined and can be hard to interpret, and because a copyright lawsuit can be extremely expensive, many users are scared or reluctant to rely on fair use when they use copyrighted works. This, in turn, has led to an effort by some groups to “reclaim fair use” for the public, and prevent what author Lewis Hyde has called “the third enclosure” of the common, that of the mind.