The age of a woman who appears to be in her 40's or above, but claims to be or alludes to being much younger.
Also may hang out with people in their 20's on a regular basis, thinking that she fits in.
Term originated from the last name of faux-Australian-celebrity, Amber Petty.
Q: How old is that new cougar that works in advertising over there?
A: About Petty-Seven!