RoShamBo is the game of Rock-Paper-Scissors, the classic simultaneous decision game. Face to face, players count to three, then simultaneously display either a fist for rock, open hand for paper, or two fingers for scissors. Scissors defeats paper which defeats rock which defeats scissors.
This is usually played multiple times to allow strategy to come into it. Even though a completely random choice is no less likely to win against any strategy, it is also no more likely to win, while a better strategy will defeat a worse strategy.