Definition of "callback"

callback

noun
plural callbacks
1. The return of a situation to a previous position or state.
  Quotations
  Aiden Gillen whimpers on his knees, stretching for the first time in years. And finally Sansa sentences him, and Arya swings the sword, or dagger as the case may be. For all the historical callbacks in the episode, and in its old age Game Of Thrones keeps portentously reciting old lines verbatim, this callback is the most resonant. Ned always said the man who passes the sentence should swing the sword. His daughters are finding a different way forward.
  2017 August 27, Brandon Nowalk, “Game Of Thrones slows down for the longest, and best, episode of the season (newbies)”, in The Onion AV Club‎
2. (telephony) A return telephone or radio call; especially one made automatically to authenticate a logon to a computer network.
  Quotations
  For example, multiple callbacks might be made to a nonanswered number to increase the response rate.
  2007, James M. Lepkowski, Clyde Tucker, J. Michael Brick, Advances in Telephone Survey Methodology, page 318
3. A product recall because of a defect or safety concern.
4. (programming) A function pointer passed as an argument to another function.
  Quotations
  Historically, all viable frameworks have always provided a mechanism to implement callbacks. C# goes one step further and encapsulates callbacks into callable objects called delegates.
  2010, Trey Nash, Accelerated C# 2010, page xxvi
5. (theater) A follow-up audition in casting.
6. (comedy) A joke which references an earlier joke in the same routine.
  Quotations
  When the album succeeds, such as on the swaggering, Queen-esque “Nothing’s Gonna Stop Us,” it does so on The Darkness’ own terms—that is, as a random ’80s-cliché generator. But with so many tired, lazy callbacks to its own threadbare catalog (including “Love Is Not The Answer,” a watery echo of the epic “I Believe In A Thing Called Love” from 2003’s Permission To Land), Hot Cakes marks the point where The Darkness has stopped cannibalizing the golden age of stadium rock and simply started cannibalizing itself. And, despite Hawkins’ inveterate crotch-grabbing, there was never that much meat there to begin with.
  2012 August 21, Jason Heller, “The Darkness: Hot Cakes (Music Review)”, in The Onion AV Club‎
7. A form of audience participation in which the audience shout lines in response to the dialog of a film.
  Quotations
  Apparent on this disc is the problem that plagues every recording of the score: Without an audience full of rowdy geeks screaming out callbacks, Rocky Horror feels incomplete.
  2004, Michael Portantiere, The Theatermania Guide to Musical Theater Recordings, page 310