Fair Use is a integral part of US Copyright law.
What is deemed “fair use” is determined by these factors:
- Purpose and character of the use, including whether the use is of a commercial nature or is for nonprofit educational purposes
- Nature of the copyrighted work
- Amount and substantiality of the portion used in relation to the copyrighted work as a whole
- Effect of the use upon the potential market for or value of the copyrighted work
The official complete statements from the United States Government are found at:
https://www.copyright.gov/fair-use/