Definition of skidmark:
(n) :
(colloquial, humorous, euphemistic) A visible feces stain left on underpants, trousers, or sometimes the toilet bowl.
(n) :
A long black mark left on a road surface from the sliding or skidding tires of a motor vehicle that has lost traction.
(n) :
Any other mark or stain caused by one surface skidding along another.