Here's what wikipedia has to say on their page on "Age disparity in sexual relationships" (see http://en.wikipedia.org/wiki/Cougar_...29#Slang_terms):

Cougar—a woman over 40 who sexually pursues younger men, typically more than eight years her junior. The term appears to have been coined by Canadian website Cougardate.com and has been used in TV series, advertising and film. The 2007 film Cougar Club was dedicated to the subject and in Spring 2009 TV Land aired a reality show called The Cougar.