4D film or 4-D film is a marketing term for an entertainment presentation system combining a 3D film with physical effects that occur in the theatre in synchronization with the film. Effects simulated in a 4D film may include rain, mist, bubbles, fog or smoke, wind, temperature changes, strobe lights, scent, vibration and motion. Seats in 4D venues may vibrate or move a few centimeters during the presentations. Other common chair effects include air jets, water sprays, and leg and back ticklers. Auditorium effects may include smoke, rain, lightning, bubbles, and smell.
Because physical effects can be expensive to install, 4D films are most often presented in custom-built theatres at special venues such as theme parks, amusement parks and zoos. However, some movie theatres have the ability to present 4D versions of wide-release 3D films. The films Journey to the Center of the Earth (2008) and Avatar (2009) are among the films that have received a 4D treatment in certain theatres. There are also mobile 4D theaters, which are mounted inside vehicles such as enclosed trailers, buses and trucks.
4D films are distinct from four-dimensional space. Notable historical formats for providing different aspects of a "fourth dimension" to films include Sensurround, and Smell-O-Vision. As of June 2015, about 530 screens worldwide have installed some 4D technology.