Off West End refers to theatres in London which are not included as West End theatres. The term is a relatively recent one, coined after the similar American term "off-Broadway" (though without the same strict definition). It is usually used synonymously with the more widespread term Fringe (or, specifically, "the London Fringe"), but sometimes is also used to refer to more mainstream or commercial theatre which is located within London but outside the centre, or to especially small and non-commercial theatres located within the centre. According to London Theatre, "Smaller theatres, including many pub theatres, are called Fringe, although some of these small theatres are also called Off West End, particularly those located in the West End of London, where most of the big commercial theatres are. These small theatres can vary in size, with seating capacities of around 40 to 400."

While West End Theatres must register with the Society of London Theatre, SOLT membership for the Off West End is entirely optional and is not widespread. The industry organisation for Off West End and Fringe venues is the Society of Independent Theatres.