For the city in Texas see Anahuac, Texas

Anahuac is a geographical district of Mexico, limited by the traditional and vaguely defined boundaries of an ancient Indian empire or confederation of that name previous to the Spanish conquest. The word is said to signify "country by the waters" in Nahuatl, the old Aztec language; hence the theory that Anahuac was located on the sea coast. One of the theories relating to the location of Anahuac describes it as all the plateau region of Mexico, with an area equal to three-fourths of the republic, and extending between the eastern and western coast ranges from Rio Grande to the isthmus of Tehuantepec. A more exact description, however, limits it to the great plateau valley in which the city of Mexico is located, between 18°40' and 20°30'N latitude, about 320 kilometers (200 miles) long by 120 kilometers (75 miles) wide, with an average elevation of 2300 meters (7500 feet), and a mean temperature of 17°C (62°F). The accepted meaning of the name fits this region as well as any on the sea coast, as the lakes of this valley formerly covered one-tenth of its area. The existence of the name in southern Utah, United States, and on the gulf coast of Mexico, has given rise to theories of other locations and wider bounds for the old Indian empire.

(from an old encyclopedia)