Originally a mythological homeland. In contemporary times it is used as a rallying cry for ethnic seperatists, angry that conquerors came along and conquered the area from conquerors who had previously conquered it from the original group of conquerors.
Chicano activist: "Aztlan is the rightful homeland of my people"
Informed person: "Which people? The Pueblo nations? Chichimechs? Tarascans? Aztecs? Spanish? Commanche? Mestizo?"