A pocket is where the bottom of a girls ass folds over the top of her thigh whenever she takes a step. You usually have to have a decent ass to have this, and because of that a good way to rate female ass is by checking if they have a pocket.
dude that girls pockets so big i can put my spare change in it
dude, dude, dude its like totally when someone tries to masturbait through their pocket without anyone noticing
(but someone will notice when the dude has a cream of wheat)