Cottaging is the act of anonymous sex in a public lavatory or of picking a stranger up in a public lavatory to go and have sex elsewhere. The term is predominantly British, a 'cottage' being a small free-standing building housing public toilets, though it is occasionally used in other parts of the world. In America lavatories used for this purpose are called Tea Rooms.
Cottaging is more common among gay men, though it occurs among people of all sexes and sexual orientations. In the United Kingdom the act of cottaging itself is not against the law, though related charges of gross indecency and indecent exposure may be brought, especially if the two people caught in the act are both men.