Buck buck (also known as Johnny-on-a-Pony, or Johnny-on-the-Pony) is a children's game with several variants. One version of the game is played when "one player climbs another's back" and the climber guesses "the number of certain objects out of sight". Another version of the game is played with "one group of players [climbing] on the backs of a second group in order to build as large a pile as possible or to cause the supporting players to collapse."

As early as the 16th century, children in Europe and the Near East played Buck, Buck, which had been called "Bucca Bucca quot sunt hic?" Pieter Bruegel's painting Children's Games (1560) depicts children playing a variant of the game.

In the United Kingdom, the game is sometimes called High Cockalorum, but has a large number of different names in various local dialects. These include: "Polly on the Mopstick" in Birmingham, "Strong Horses, Weak Donkeys" in Monmouthshire, "Hunch, Cuddy, Hunch" in west Scotland, "Mont-a-Kitty" in Middlesbrough, "Husky Fusky Finger or Thumb" in Nottinghamshire, "High Jimmy Knacker" in east London, "Jump the Knacker 1-2-3" in Watford, "Wall-e-Acker" or "Warny Echo" in north West London, "Stagger Loney" in Cardiff, "Pomperino" in St Ives, Cornwall and "Trust" in Lancashire. The game is sometimes played in the sergeants' or officers' messes of the British Armed Forces.