Ongoing gay themed parties held in major metropolitan areas, circuit parties originated during the heydays of the rave scene back in the early-to-mid 90's. Crowds at these parties are huge, usually numbering in the tens of thousands, and are almost all male. Many of the attendees wear next to nothing, and drug use is often rampant.
Such parties are often charity fund raisers for AIDS research and other GLBT issues, and as such usually have enormous cover charges (typically at least $100). They will often go on for several days at any given venue, and when one stops, another one usually starts. Regular attendees are frequently referred to as circuit boys, a term that carries a fair amount of negative connotation in many gay communities.