What is "tower defense"

n. (context video games English) A style of real-time strategy video game in which the player attempts to stop enemies from crossing a map by building traps to slow them down and towers or turrets which shoot at them as they pass within range.

Tower defense (or informally TD) is a subgenre of strategy video game where the goal is to defend a player's territories or possessions by obstructing enemy attackers, usually achieved by placing defensive structures on or along their path of attack. This typically means building a variety of different structures that serve to automatically block, impede, attack or destroy enemies. Tower defense is seen as a subgenre of real-time strategy video games, due to its real-time origins, though many modern tower defense games include aspects of turn-based strategy. Strategic choice and positioning of defensive elements is an essential strategy of the genre.