rock paper scissors

Short definition from Wiktionary

Noun

1. 1
   A popular children's game using three hand signs representing rock, paper and scissors, frequently used as a tiebreaker.
2. 2
   Any situation where strategies are not transitive, meaning each strategy is strong against some strategies and weak against others in a loop such that there is no universally best option.
3. 3
   Alternative spelling of rock paper scissors.

Verb

1. 1
   To play a round of Rock–paper–scissors.