Piece of cloth or clothing used to wipe the jism off one's belly after masturbating. Generally unwashed and stored under the bed, the foul towel develops an ungodly odor and becomes rigid after several uses. May be able to stand on it's own with enough use. Often used by a towel wanker. See also wank towel or gak towel.
I ran out of tissues, so I had to use my shirt as a foul towel.