"Fair Use" is a doctrine in U.S. copyright law allowing limited use of copyrighted material without requiring permission from copyright owners.
Some examples of fair use are for commentary, criticism, news reporting, research, and teaching or scholarship. To learn more about fair use, please visit this page from www.copyright.gov.
A similar principle, "Fair Dealing", exists in some other common law jurisdictions such as Canada. To learn more about Canadian Copyright law, you can view their Copyright Act here.
Please note that copyright law is different in every territory. Please check your local laws as necessary.