To sneak behind someone's back in the hopes of catching them unaware. A term popularized in gaming communities that has two definitions depending on the context:
1) On TV shows like Big Brother and Survivor, a backdoor tactic involves playing an item that grants a player immunity on the agreed upon target at the latest possible moment. This makes it so that the actual target who you plan to vote for, to eliminate, has as little time as possible to scramble to get enough votes to keep themselves alive in the game. Keeping them in the dark about the plan to eliminate them until the latest moment also may make them less likely to try harder in challenges, mistakenly believing they'll be safe, when in actuality they're the one being targeted. This is similar to a "blindside", but to "backdoor" someone refers specifically to a plan that involves removing someone who is in danger off the chopping block and setting up another player for elimination.
2) In MOBAs like League of Legends, a backdoor is a tactic that usually involves one strong player splitting away on their own with the goal of sneaking behind enemy lines while the enemy team is distracted elsewhere and destroying their base (specifically their nexus) to win the game before they can react in time to stop you. Made famous by xPeke who infamously backdoored SK Gaming with Kassadin.
1) On TV shows like Big Brother and Survivor, a backdoor tactic involves playing an item that grants a player immunity on the agreed upon target at the latest possible moment. This makes it so that the actual target who you plan to vote for, to eliminate, has as little time as possible to scramble to get enough votes to keep themselves alive in the game. Keeping them in the dark about the plan to eliminate them until the latest moment also may make them less likely to try harder in challenges, mistakenly believing they'll be safe, when in actuality they're the one being targeted. This is similar to a "blindside", but to "backdoor" someone refers specifically to a plan that involves removing someone who is in danger off the chopping block and setting up another player for elimination.
2) In MOBAs like League of Legends, a backdoor is a tactic that usually involves one strong player splitting away on their own with the goal of sneaking behind enemy lines while the enemy team is distracted elsewhere and destroying their base (specifically their nexus) to win the game before they can react in time to stop you. Made famous by xPeke who infamously backdoored SK Gaming with Kassadin.
Rob: So, everyone is on board to backdoor Russell?
Sandra: Yes. Play your immunity idol on me tonight, Rob, and we'll all backdoor his dirty ass out of this game.
Rob: I can't wait to see his face when he realizes he's being backdoored.
Sandra: He's so stupid, he probably won't realize what's going on until after Jeff snuffs out his torch.
Sandra: Yes. Play your immunity idol on me tonight, Rob, and we'll all backdoor his dirty ass out of this game.
Rob: I can't wait to see his face when he realizes he's being backdoored.
Sandra: He's so stupid, he probably won't realize what's going on until after Jeff snuffs out his torch.
by scotstee April 6, 2022
Get the Backdoormug. 
by Travmanicas March 4, 2007
Get the Backdooredmug. The act of putting yourself in a position that furthers you from your optimal goal. Doing something even though you know that it is not helping you in life and instead it is holding you back.
I'm really backdooring myself... I failed a test because instead of studying the night before I went out and got wasted.
by the bbbear July 18, 2010
Get the backdooringmug. 
by demmahom November 17, 2018
Get the backdooringmug. White Guy : *Not paying attention to anything*
Black Guy 1: *Runs at extreme speeds and hits white guy in the back of the head.*
Black Guy 2: "DAMN! He just backdoored the shit outta that white guy!!"
Black Guy 1: *Runs at extreme speeds and hits white guy in the back of the head.*
Black Guy 2: "DAMN! He just backdoored the shit outta that white guy!!"
by Hyrohimaru May 31, 2010
Get the backdooredmug.