Fair Use is the provision of U.S. copyright law that allows the use of copyright protected works without the permission or authorization of the copyright owner. Under fair use certain types of uses are not infringements. Copyright owners may not like your use, may wish that you didn't use the work the way you did but if your use meets the four factor test that considers:
The purpose of your use
The nature of the original work your used
The amount of the original work you used
The effect of your use on the market, or potential markets for the original work
Then it could be that your use is a fair use and there's not a lot the copyright owner can do about it.
So, not much help really, right? The dictionary is only just beginning.