Definition from Wiktionary, the free dictionary
From French frotter (to rub).
- To rub, especially to rub onto one surface placed upon another surface that is textured, in order to create a mottled or patterned area on the first surface.
- (uncountable, art) A method of making an image by placing a piece of paper against an object and then rubbing over it, usually with a pencil or charcoal.
- (countable, art) An image so made.
- (uncountable, sexology) The practice of rubbing parts of the body against those of a consenting partner for sexual stimulation.
- (sexology): tribadism
Coordinate terms 
- (sexology): frotteurism