A turnstile is a gate which allows one person to pass at a time. It can also be made so as to enforce one-way traffic of people. In addition, it can limit passage exclusively to people who insert a card, 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) or to allow access exclusively to authorized people, for example in the lobby of an office building.

From a business point of view, turnstiles give an accurate, verifiable count of attendance. From a security point of view, they can enable authorized person to access and to keep unauthorized person away without the use of human personnel to control entries.