Burning Man is a six-day annual event that takes place in Black Rock City, a temporary city on the playa of the Black Rock Desert in the U.S. state of Nevada, 90 miles north-northeast of Reno, ending on the American Labor Day holiday in September. The event is described by organizers as an experiment in community, radical self-expression, and radical self-reliance and takes its name from the ritual burning of a large wooden effigy on the sixth day.
See more on Burning Man at the official site.
Jeff and Francine go to Burning Man after Stan erases her memory to cover for forgetting their anniversary in "Francine's Flashback". Stan and Hayley follow, where he finds her about to go on tour with a band. When he tries to confront her, she rejects him, but events knock out Francine and restore her memory.
When Jeff forgets to get tickets to Burning Man for his anniversary with Hayley in "Camp Campawanda", Roger tries to help them out by throwing his own in the Smith's backyard, causing Hayley to becomes suspicious of his motives. When evidence appears to make it look like he intends to harvest their organs, they confront him where he reveals that he harvested his own organs to pay for the celebration.