Green’s Dictionary of Slang

(US) the buttocks.

1882		Nat. Police Gaz. (NY) 8 Apr. 2/2: Anna always was a girl of solid understanding, though, so you needn't be so fresh in crying ‘Pads’.
1971		(con. 1930s) D. Wells Night People 71: That chick you had last Friday sure did have a broad understanding! Boy, was she stacked!