Usualy a terry cloth or cotton towel used to wipe one's brow on hot summer days. Also used as portable shade for one's head from the sun rays. Almost always white in color. Paper towels can also be used in a pinch.
Brotha be drivin down the road on some hot shit, and needs to wipe his nappy ass mug.
"Shit it's hotter than a mug, son. Wish I woulda brought my baby mama' sweat towel"