This video from the U.S. Copyright Office outlines the tenets of fair use and where it might and might not apply. Below the video are some examples of copyright infringement cases that have involved fair use claims, so you can see real-life examples of its application and interpretation.
"It's fair use because it's educational!"
This is the most common fair use argument on a college or university campus, but just because a copyrighted work is used in an educational context does not mean the use is fair. This Fair Use Checklist from the University of Chicago provides a set of criteria that can push a use from fair to foul and back again.
Summaries of Fair Use Cases (Stanford University) Explore cases involving text, media, music, online content, and parody in this excellent summation by lawyer Rich Stim.
Of particular note for higher ed and music are: