A turnstile, also called a baffle gate, is a form of gate
A gate is a point of entry to a space enclosed by walls, or a moderately sized opening in a fence. Gates may prevent or control entry or exit, or they may be merely decorative. Other terms for gate include yett and port...

 which allows one person to pass at a time. It can also be made so as to enforce one-way traffic of people, and in addition, it can restrict passage only to people who insert a coin, a ticket, a pass, or similar. Thus a turnstile can be used in the case of paid access (sometimes called a faregate when used for this purpose), for example public transport
Public transport
Public transport is a shared passenger transportation service which is available for use by the general public, as distinct from modes such as taxicab, car pooling or hired buses which are not shared by strangers without private arrangement.Public transport modes include buses, trolleybuses, trams...

 as a ticket barrier or a pay toilet
Pay toilet
A pay toilet is a public toilet that requires money payment of any individual to use. It may be street furniture or be inside a building, e.g. a mall, department store, railway station, restaurant, etc. The reason for charging money for using toilets usually is for the maintenance of the...

, or to restrict access to authorized people, for example in the lobby of an office building.

Turnstiles are used at a wide variety of settings, including stadiums, amusement parks, museums, mass transit stations, office lobbies, retail sites, cafeterias, temporary exhibits, ski resorts, casinos and souvenir stands.

From a business/revenue standpoint, turnstiles give an accurate, verifiable count of attendance.