- Isthmus of, an isthmus in S Mexico, between the Gulf of Tehuantepec and the Gulf of Campeche. 125 miles (200 km) wide at its narrowest point.
- Gulf of, an inlet of the Pacific, off the S coast of Mexico. About 300 miles (485 km) wide.
- Isthmus of Tehuantepec the narrowest part of S Mexico, with the Bay of Campeche on the north coast and the Gulf of Tehuantepec (an inlet of the Pacific) on the south coast