A map represents the environment a match is played in. They contain various terrain features ranging from cliffs and caves to abandoned research centres and ancient temples. Most maps also contain various resources (like gold, iron, trees, etc.) which your army can use to produce units, research new technologies and construct buildings and installations. Maps vary greatly in size, from small ones suitably only for 2 players to large free for all maps.
Some maps are designed for one gamemode like there are arena maps, medeivil maps, defend the keep maps and much more