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.
Utilized combat systems where characters or teams take turns making their next move. Turns often have no time limit, allowing for a greater opportunity to think about strategy. The opposite of real-time combat.