Fair use is a statutory exception to the copyright holder's bundle of exclusive rights. It allows for the unlicensed (that is, without permission or payment of royalty) use of a copyrighted work where the balance of several factors weighs in favor of such use.
The four statutory factors of fair use are:
Examples of fair use in U.S. copyright law include commentary, search engines, criticism, news reporting, parody, research, and scholarship.
Several factual inquiries drive analysis of each of the four factors. Several libraries have also created excellent guides to understanding and applying the four factors: