(in basketball, football, and hockey) a system of defensive play in which each player guards an allotted area of the field of play and guards an opponent only when the opponent is in his area.
Definition of zone defense in US English:
zone defense
noun
(in basketball, football, and hockey) a system of defensive play in which each player guards an allotted area of the field of play and guards an opponent only when the opponent is in his area.