Four

Four can refer to any of the following:
 * Quattro, known in the Italian version as Four
 * Quattro (disambiguation)
 * Level 4 Monster Cards
 * Rank 4 Monster Cards
 * Link 4 Monster Cards
 * "Spell Speed 4", a fan-made term for cards in any of the following categories:
 * Activation cannot be negated
 * Effect that cannot be negated
 * Prevents responding to its activation