Gambling was the act of wagering against odds in order to profit. This often took the form of games. An individual wager could be known as a bet.
History
In 1289, in the Imperial Palace in Peking, the First Doctor wagered on a game of backgammon with Kublai Khan. After winning half of Asia, he wagered it all for the TARDIS and lost. (TV: "Assassin at Peking")
In 1881, in the Last Chance Saloon, Seth Harper, Ike Clanton and Phineas Clanton wagered on a game of cards while waiting for the appearance of Doc Holliday. (TV: The Gunfighters)
In 1963, the Twelfth Doctor gambled in Vegas, winning non-stop; he told Clara that it was simple mathematics. When taken to the owner of the casino to explain how his system worked, the Doctor explained in great detail how he always chooses the most likely probability based on all the factors of rolling dice. (COMIC: Gangland)
In 2006, in Chicago, the First Doctor gambled away the TARDIS again, this time in a game of cards with a businessman named Buchanan. He did, however, win a purple Oldsmobile 88 in another game. (PROSE: The Mother Road)
In late 2006, Mickey Smith bet that PM Harriet Jones wouldn't mention that she fought Slitheen with Rose Tyler on Question Time. (PROSE: Mars)
Several joking and rhetorical bets were placed during when UNIT officers discussed the disappearace of the Guinevere One and the subsequent alien transmissions on an operations board on the UNIT website on Christmas Eve 2006. Major Richard Blake bet that the PM would use the dissappearance of the Guinevere One to visit the Tower Ops, Sgt A. Frederick bet that the Guinevere One was just space junk, Sgt Catherine Petts bet on how long it would take before the aliens would start selling jewelry on their "TV channel", and Frederick put a tenner on it taking a week until Anthea Turner would get her own show on the channel. (PROSE: Guinevere One)
In 2294, in Venice, Duke Orsino gambled away Estella in a game of cards. (AUDIO: The Stones of Venice)