A pub quiz was a trivia contest conducted in a pub.
To learn why Mary said Toshiko Sato could call her Philoctetes instead of Mary, she asked Jack Harkness who he was. To divert suspicion, she claimed that it was a question in a pub quiz at the Prince of Tides. (TV: Greeks Bearing Gifts)
While in Cheldon Bonniface in April 2010, Bernice Summerfield, Jason Kane and their wedding party frequented the Black Swan. One night, they even participated in a pub quiz there. (PROSE: Happy Endings)
The Eleventh Doctor told Gregor Van Baalen that he wouldn't be needing him on his quiz team, after the latter failed to recognise that the TARDIS self-destruct mechanism had been a bluff. (TV: Journey to the Centre of the TARDIS)