Fair Use probably isn't what you expect. Many people throw the term around without really understanding what it is, and how to apply it appropriately. In fact, every time you make a citation under fair use, the tests must be applied. It's definitely not a cut-and-dried definition, but there are some basic rules that we can apply to help us find our way.
Section 107 of the U.S. Copyright Act governs the rules for fair use. Application of these elements is like walking a tightrope, you have to be balanced or the fall might hurt you. These elements have undergone judicial review and have withstood the test of time. These elements are explained further in this tutorial.
Whether or not fair use applies to you is dependent on these four elements:
1) The Character and Purpose of the Use.
2) The Copyrighted Work and its Nature
3) How Much of the Original Work Did You Use
4) The Impact of the Use on the Value of the Original Work
DISCLAIMER: This should not be construed as legal advice. For any issues surrounding the use of copyrighted material, the appropriate legal authority (not me) should be consulted.
Best Regards,
Jim