Short Interest is a market sentiment indicator. There's an Investopedia article on this at <a href="http://www.investopedia.com/articles/01/082201.asp" target="_blank">http://www.investopedia.com/articles/01/082201.asp</a>, and Short Selling in general with related terms at <a href="http://www.investopedia.com/terms/s/shortselling.asp" target="_blank">http://www.investopedia.com/terms/s/shortselling.asp</a>