An older woman (usually 30+) who is on the prowl for younger men usually in bars, restaurants, night clubs, or on the beach. She is always financially secure and thus isn't looking for an older man to provide for her. She may be single, married, divorced, with children, or without. No circumstance can stop her from going after her prey (young HOT and SEXY men) usually between 18 and 29. Any older just isn't her thing.
The term derived from the Hollywood Hills area of Los Angeles California. Because it is the hills where wildlife live such as cougars, deer, etc... Much like a cougar, the rich woman living in the Hollywood hills comes down the mountain to prey on young men. The younger guys usually struggling actors/waiters, starving musicians, starving students, or just starving are eager to get their drinks paid for by these ladies. They also hope these ladies will invite them back to their pad for some fun in their beautiful rich homes.
Since the term started to catch on and expand across the states the definition has been changed many times over.
However, the basic character is the same. Financially secure women over 30 years old who like younger men to marry, sleep with, or just have around for eye candy.
A single rich Cougar woman from the Hollywood Hills comes down for some fun night club time with a couple of her friends and end up taking some unemployed guys back to their house for fun.