In copyright law, fair use is a legal doctrine that allows the limited use of copyrighted material without permission from the copyright holder for purposes such as criticism, commentary, news reporting, teaching, scholarship, or research. Fair use is determined on a case-by-case basis and involves four factors: the purpose and character of the use, the nature of the copyrighted work, the amount and substantiality of the portion used, and the effect of the use on the market for the original work. It's important to note that fair use is a defense against a copyright infringement claim and is not a black-and-white rule. Courts will consider all the factors involved in each specific situation to determine if the use is fair. While fair use provides some flexibility in using copyrighted material, it's essential to understand the limitations and always consider seeking legal advice if you're unsure about whether your use qualifies as fair use.