Cottaging is a sex slang term that refers to anonymous sex that occurs between two men in a public place, often a restroom. It may also refer to the act of seeking out anonymous sexual partners. This term is most commonly used in Britain. Cottages are often restrooms, but they may be any place that's heavily used by many people. In the United States, cottages are more commonly referred to as tea rooms.
Kinkly explains Cottaging
This term gets its name from English toilet blocks which resemble small cottages. The practice is believed to have sprung up before the gay liberation movement when people needed a relatively public place to meet others who were gay. People largely found each other through signaling, such as foot taps between cubicles. Sex in a public place is illegal in most jurisdictions, however. As a result, many highly trafficked cottages in Britain have been retrofitted with high cubicle walls to prevent communicaton between stalls.