body slide

what exactly is this thing called a body slide? what are the characteristics when this thing is done superbly?

can some one explain to me how does a girl rubbing her ass on your dick, make you cum? with body slide do you get any HJ, BJ??? or just her ass touching your boys? 1)i find it hard to believe it would make you cum 2)it cost about the same as fs, perhaps more but i have to agree, alot of...