Fair use is a copyright principle based on the belief that the public is entitled to freely use portions of copyrighted materials forpurposes of commentary, criticism, reaserch and education.
Fair use is not an exception to copyright compliance; it is more of a "legal defense." That is, if you copy and share a copyright-protected work and the copyright holder claims copyright infringement, you may be able to assert a defense of fair use which you would then have to prove.
Fair use is primarily intended to allow the use of copyright-protected works for commentary, parody, news reporting, research and education. However, not all uses in an academic context are automatically considered fair use.
The only guidance in determining whether the use of copyright-protected work is a fair use is provided by a set of factors outlined in the copyright law. Unfortunately, weighing the fair use factors is often quite subjective. For this reason, the fair use road map is often tricky and hard to navigate. To avoid a potential legal challenge from the copyright holder, many institutions follow a policy of "when in doubt, obtain permission."
For some more help thinking about how your class materials fit into this complex section of the copyright law, you might visit the University of Texas' Crash Course in Copyright
