The concave area that is located beneath the shoulder and arm, also known as the armpit. Closely related to the wenis and the wagina.
A father is explaining the anatomy of the human arm to his son.
Father - "Well son, this here flap o' skin on yer elbow be yer wenis, and the thing on the other side be yer wagina."
Son - "But Pa, what be this here thing under yer arm?"
Father - "Under me shoulder? Oh, that just be me wutthole, son."