Cohabitation is an arrangement where two people are not married but live together. They are often involved in a romantic or sexually intimate relationship on a long-term or permanent basis. Such arrangements have become increasingly common in Western countries since the late 20th century, being led by changing social views, especially regarding marriage, gender roles and religion.
More broadly, the term cohabitation can mean any number of people living together. To "cohabit", in a broad sense, means to "coexist". The origin of the term comes from the mid 16th century, from the Latin cohabitare, from co- 'together' + habitare 'dwell'.