The Tower Defense Games
Tower defense is began in 1990, a subgenre of real time strategy computer games. Tower defense games are characterised by the positioning of static units by the player to defend against mobile enemy units who are trying to get from a start point to an end point.
The goal is to try to stop enemies from crossing the map by building towers which shoot at them as they pass. Enemies and towers usually have varied abilities and costs. When an enemy is defeated, the player earns money or points, which are used to buy or upgrade towers.