Unidentified Party Wound. An injury or bruise received over the course of an evening of drinking with no recollection of how it occurred. Generally self-induced due to one's stupidity and involving a fall, stumble or collision with an inatimate object.
"I woke up this morning with a huge U.P.W. on my thigh.... I remember smashing into a table, but one of my friends told me I fell trying to get into a cab…..I guess I’ll never know"
by R.D.P. April 14, 2007