4X is a genre of strategy-based games in which players control an empire and "eXplore, eXpand, eXploit, and eXterminate". Emphasis is placed upon economic and technological development, as well as a range of non-military routes to supremacy. Games can take a long time to complete since the amount of micromanagement needed to sustain an empire increases as the empire grows.
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.
