A turnstile is a mechanical gate consisting of revolving horizontal arms that allow entry or exit in a controlled manner. Commonly found in places like subways, amusement parks, and stadiums, turnstiles help manage the flow of people and ensure that only authorized individuals can pass through. They often require a ticket or card to unlock the mechanism. Turnstiles can be manual or electronic, with electronic versions often equipped with sensors and ticket readers. They enhance security by preventing unauthorized access and can also track the number of people entering or exiting a location, providing valuable data for management and safety purposes.