A lost city is an urban settlement that fell into terminal decline and became extensively or completely uninhabited, with the consequence that the site's former significance was no longer known to the wider world. The locations of many lost cities have been forgotten, but some have been rediscovered and studied extensively by scientists. Recently abandoned cities or cities whose location was never in question might be referred to as ruins or ghost towns. Smaller settlements may be referred to as abandoned villages. The search for such lost cities by European explorers and adventurers in Africa, the Americas, and Southeast Asia from the 15th century onwards eventually led to the development of archaeology.

In geography, statistics and archaeology, a settlement, locality or populated place is a community of people living in a particular place. The complexity of a settlement can range from a minuscule number of dwellings grouped together to the largest of cities with surrounding urbanized areas. Settlements may include hamlets, villages, towns and cities. A settlement may have known historical properties such as the date or era in which it was first settled, or first settled by particular people. The process of settlement involves human migration.