A back door is a door in the rear of a building. Back door may also refer to:

• Back Door (jazz trio), a British group
• Porta dos Fundos (literally “Back Door” in Portuguese) Brazilian comedy YouTube channel.
• Works so titled:
  • The Back Door (fiction), a 1897 work serialised in Hong Kong
  • "Back Door", a 1969 sound single by Rhinoceros (band)
  • Musical albums:
    • Back Door (album), a 1972 by English jazz trio Back Door
    • The Back Door (album), a 1992 album by American band Cherish the Ladies
  • Songs:
    • "Back Door", a 2020 song by South Korean boy group Stray Kids from the album In Life
    • "Backdoor" (song), a 2020 song by American rapper Lil Durk
    • "Back Door", a 2021 song by American rapper Pop Smoke from the album Faith

• Backdoor (computing), a hidden method for bypassing normal computer authentication systems
• Backdoor (basketball), a play in which a player gets behind the defense and receives a pass for an easy score
• Backdoor Bay, Ross Island, Antarctica
• Slang for the human anus
• Slang for doing something in a secret, dishonest, or indirect way, often used as a pejorative.

• Backdoor pilot, the use of existing series in assessing potential audience reaction to a proposed television series
• Backdoor breaking ball, a type of pitch
• Backdoor.Win32.IRCBot, a computer worm
• Music:
  • Backdoor progression, in music theory, characteristic harmonic device used in many "jazz standards"
  • Works:
    • "Back Door Man", a 1960 blues song, written by Willie Dixon & recorded by Howlin' Wolf
    • "Back Door Santa", a 1968 blues song written by Clarence Carter and Marcus Daniel
    • "Lookin' out My Back Door", a rock song by Creedence Clearwater Revival, on their 1970 album Cosmo's Factory