During the 1950's and 1960's, the Boston Celtics basketball team had an all-star point guard named Bob Cousy who was known for his extraordinary ball-handling ability. He was particularly famous for dribbling the basketball between his legs - a fete that required him to squat (usually, although he could do it on the run too) and spread his legs wide to get the ball through. His knickname was "The Cooz" - and around New England women who spread their legs far enough to see things they were taught to keep far from prying eyes were thought to be mimicking Bob Cousy's between-the-legs dribble, thus revealing the old "cooz."
Wow! Take a gander at the cooz on the broad sittin' over there on the couch!
A girl who is the perfect dick fit. The term comes from the word coozie, sn item that conveniently fits around a beer bottle. Therefore, a cooz is a girl who is convenient to bang, and seems to be made for your dick.
That girl is such a cooz; our genitalia fits together like macaroni and cheese.