A person who takes unauthorized possession of unoccupied premises or land, usually to live there.

In the USA, from the late 18th century, a squatter was a settler having no normal or legal title to the land he occupied, particularly in a district not yet surveyed.

In New South Wales, Australia, the term was applied from the early 19th century to those, often ex-convicts, who occupied land without authority and stole stock. By the 1830s, its meaning had begun to broaden, often being applied to the many pastoralists settling beyond the official 1829 limits of settlement. They were mostly involved in the wool industry, and in 1836 were granted grazing rights for an annual licence fee. The squatters demanded security of tenure and pre-emptive rights, which they gained in 1847, securing the land most suitable for agricultural and pastoral purposes. Thereafter squatters became a very powerful group, socially, economically, and politically; they often struggled bitterly over land with selectors during the second half of the 19th century. Squatters continued to be known by that name even after they acquired their land freehold. Eventually, the term was applied to all large pastoralists in Australia.

Squatting nowadays generally results from housing shortages, but whereas in rich countries squatters tend surreptitiously to take single buildings, in poorer ones the illegal occupation of land is on so great a scale that the authorities often condone it and sometimes grant squatters legal title.