If someone accuses you of copyright infringement, you can defend the charges by proving that your activity is covered by Section 107 of the Copyright Act, which provides some protection from allegations of copyright infringement "for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research."
Defenders of fair use are sometimes painted as anti-business, because they generally believe in shorter copyright terms and other measures designed to revert intellectual property into the public domain after it has been exploited by its original owner (this span has been lengthened periodically by what's known as the "Mickey Mouse law").
But according to a study (PDF) released last week by the Computer and Communications Industry Association (CCIA) using methodology devised by the World Intellectual Property Organization (WIPO), the "fair use economy" generated over $4.5 trillion last year, representing about one sixth of the entire US gross domestic product for 2006 and employing millions of Americans.
Ed Black, President and CEO of CCIA, said that providing a clearer legal right to fair use would grow the creative segments of our economy:
(via mi2n)