Survivor is an American reality TV series where strangers are split into tribes and dumped into the wilderness to compete for a $1,000,000 prize.
A lot of twists have been introduced over 20 seasons, but Survivor's basic formula remains the same. Take between 16 and 20 Americans of various races, ages, and genders. Split them into 2-4 tribes, give them a map and some basic supplies, and send them into the wilderness (locales have included Kenya, China, Micronesia, Thailand, Australia, Gabon, the Amazon, Pearl Islands, and many more) to "survive." They often have to go the first three days without fire (and therefore clean water) unless they can build it themselves. They build their own shelter with supplies found in the area, and they're sometimes supplied with rice but it's up to them to seek food beyond that. Survivor: The Australian Outback starved its participants until The View's Elisabeth Hasselbeck's hair was falling out and she was forced to catch and eat crickets.
The key to survival is immunity, which prevents a tribe from going to Tribal Council where they have to vote off a member. Tribal Council occurs every three days, except when there is a rare double elimination or a player is removed from the game due to injury (like when Mike Skupin fell in the fire and skin was melting off his hands) or sheer lameness (winners never quit, and quitters never win $1,000,000). Immunity in the first half of the game protects the whole tribe, but post-merge, immunity only protects one lucky person. In recent seasons, Hidden Immunity Idols have also been used. The person who finds the idol is able to save him- or herself, or assign it to someone else, and avoid going home. In cases where an HII is used, the person with the second-highest number of votes is sent packing. This results in a lot strategy--and amusing butthurt.
The tribes remain separate and compete against each other for rewards (such as food, trips, and new cars) and immunity until there are ten contestants left. They then merge and live together, competing for individual immunity. Alliances are broken and rebuilt, but the people who survive are usually those who stick with their original alliances or, if they were not in an original alliance, are able to form strong bonds with the members of the opposite team. It's usually a major advantage to enter the merge with numbers on your side (six of you versus four of them, at least).
The producers have tried all sorts of unique and interesting ways to split the tribes in new ways. We had our first men vs. women season in Survivor: The Amazon (season six), the two oldest contestants chose their tribes in a schoolyard pick format in season five (Thailand), and an Outcast Tribe was formed by ousted members in Pearl Islands (season seven). There have been some seriously ridiculous and controversial divisions, too: Exile Island (season 12) featured four tribes--older men, younger men, older women, younger women, and Cook Islands (season 13) also had four, but divided by race--Asians, African Americans, Hispanics, and Caucasians. There have also been four seasons where past survivors returned to compete against each other, or against fans: Survivor: All Stars (season eight), Survivor: Guatemala--The Mayan Empire (season 11--two survivors from the previous season returned to try again) Survivor: Fans vs. Favorites (season 16, also called Survivor: Micronesia), and Survivor: Heroes vs. Villains (season 20).