The Southwestern United States (also known as the American Southwest or simply the Southwest) is a region of the United States defined in different ways by different sources. Broad definitions include nearly a quarter of the United States, including Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas, and Utah. Narrowly defined, the "core" Southwest is centered on the Four Corner states, with parts of the other states making up the beginnings and endings of the Southwest. The five main southwestern states, Arizona, New Mexico, Colorado, Utah, and Nevada, are also all considered part of the Mountain West as well as the Southwest. Using the broad definition, the total population of these states is roughly 19 million people.