Copyright is a legal right that protects original works of authorship, such as books, music, movies, and software. It gives the copyright owner the exclusive right to reproduce, distribute, perform, display, and create derivative works from the copyrighted work.

Fair use is a legal doctrine that allows limited use of copyrighted material without permission from the copyright owner. Fair use is often used by journalists, educators, and researchers to quote or cite copyrighted material in their work.

The four factors that courts consider when determining whether a use is fair use are:

1. The purpose and character of the use, including whether it is commercial or noncommercial 
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
4. The effect of the use on the potential market for or value of the copyrighted work

No one factor is determinative, and courts will weigh all four factors in each case. However, some uses are more likely to be considered fair use than others. For example, uses that are for noncommercial purposes, such as education or research, are more likely to be considered fair use than uses that are for commercial purposes.