Game theory is the branch of mathematics in which games are studied: that is, models describing human behaviour. This is a glossary of some terms of the subject.

${\displaystyle \sigma \ _{i}}$ is an element of ${\displaystyle \Sigma \ ^{i}}$.

${\displaystyle \sigma \ _{-i}}$ an element of ${\displaystyle \Sigma \ ^{-i}=\prod _{j\in \mathrm {N} ,j\neq i}\Sigma \ ^{j}}$, is a tuple of strategies for all players other than i.

A game in normal form is a function:

Given the tuple of strategies chosen by the players, one is given an allocation of payments (given as real numbers).

A further generalization can be achieved by splitting the game into a composition of two functions:

the outcome function of the game (some authors call this function "the game form"), and:

the allocation of payoffs (or preferences) to players, for each outcome of the game.