Definition from Wiktionary, the free dictionary
cougar (plural cougars)
- A mountain lion; Puma concolor.
- (North America, slang) A woman of middle age who actively seeks the casual, often sexual, companionship of younger men, typically less than 35 years old; by implication a “sexual predator”.
- A cougar approached Warren at the Palomino Club and asked for a dance.
- (Puma concolor): Florida panther (a subspecies of mountain lion)
Coordinate terms 
- (middle-aged man who seeks younger partners): manther
slang: woman of middle age who seeks younger men