A type of game where the player builds defensive structures to stop waves of enemies from reaching and destroying their base. Towers can be equipped with many kinds of weapons, but generally are unable to move. Resources earned by defeating enemies allow for more towers to be built.
A turn-based game mechanic is the opposite of a real-time game mechanic. In a Turn-By-Turn mechanic (synonym), each player has to wait for the other to have played, so that they can play, and so on. This way, each player has the time to think about their strategy. TBT games rely less on action than real-time games.
