A law of the United States
Fair use is a doctrine that allows limited use of copyrighted material without having to acquire permission from the copyright holder. A set of guidelines are provided for researchers, educators, scholars, and others that want to use copyrighted works without seeking permission or paying royalties. This does not provide a right to use the work of someone else, but presents a defense against accusations of copyright violation for people who believed that their use of a copyrighted work was fair use. That means that if your use is challenged, you will have the burden of proving that your use qualified as "fair use".