The backdoor technique, also known as the six-finger plan, is a strategic move devised by Marvin Latimer and Nakomis Dedmon and executed by the latter in Big Brother 5 (US). It requires the Head of Household not nominating the intended target to be evicted, choosing instead to nominate two pawns, at the nomination ceremony in order to prevent the target from being guaranteed to play in the Power of Veto competition. Provided the intended target does not play in the Veto competition, the POV holder would then remove a pawn from the block, and the HOH would place the intended target on the block to be subsequently evicted. Despite debate among fans, it is generally agreed that a true backdoor only happens when the target DOES NOT play in the Veto competition.
It is a difficult technique to pull off, but if one has a group large enough to carry it out, a backdoor can be performed. It requires having 6 players to agree with the plan, and enough non-HOH and non-nominee houseguests to want to evict the target.
The backdoor was further complicated in Big Brother All-Stars (US) onwards when houseguests no longer selected players for the Veto competition but instead drew names from a bag randomly. If the target plays in the Veto competition and loses, then they become the replacement nominee, but the plan would no longer be a successful backdoor as the target would have played in the Veto competition.
Though surviving a backdoor plan is extremely difficult, it is possible. Such a feat was notably accomplished by Eric Stein on Big Brother 8 (US). Vanessa Rousso of Big Brother 17 (US) also survived the block after initially being kept off and is mistakenly noted as having "survived a backdoor". However, because she played in the Veto competition, she would not have been backdoored. Nicole Anthony survived a backdoor in Big Brother 21 (US).
Cody Nickson of Big Brother 19 (US) is notable for being backdoored twice in one season. Having been evicted through a backdoor by Paul Abrahamian in Week 2 and then winning the Battle Back Competition in Week 4, he eventually got backdoored once again by Alex Ow in Week 7.