Mustang is the term used for the free-roaming horses of the American west that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but because they are descended from once-domesticated horses, they are properly defined as feral horses. The original mustangs were Colonial Spanish horses, but as the regions of North America where they flourished were settled they, for the most part, disappeared. Most of today's mustangs are found in the Great Basin and descend mostly from unclaimed ranch stock and other non-Iberian sources such as cavalry horses released onto the federally owned lands in the Western United States. A few free-roaming horses are relatively unchanged from the original Spanish stock, most strongly represented in the most isolated populations.