4-D film is a marketing term that describes an entertainment presentation system combining a 3-D film with physical effects in the theatre, which occur in synchronization with the film (note that 4-D films are not actually, geometrically, 4-dimensional). Due to the fact that physical effects can be expensive to install, 4-D films are usually presented only at special venues, such as theme parks and amusement parks. However, in Mexico, Hong Kong, Nepal, South Korea, and India, some movie theatres also have the ability to present a 4-D film, and the film Avatar was one of 10 films that have received the treatment, starting with Journey to the Center of the Earth. Some of the effects simulated in 4-D films include rain, wind, strobe lights, and vibration. The use of water sprays and air jets is also common. A 4-D film is not shown in a motion simulator, although some seats in 4-D venues vibrate or may move a few inches during the presentation.
Due to the fast growth of movies, video, and the entertainment industry, 3-D Theatres have been enhanced by the addition of special simulations. The combination of 3-D movies with chair movement (vibration, sway, tilt, drop, wave motion, or movement in any direction) and other chair effects, such as wind blowing, water spraying, leg and back ticklers, is usually considered a 4-D experience. Using additional hall effects, such as smoke, rain, lightning, air bubbles, and special smells (for example, fireworks smells at the London Eye's Experience and gassy smells, when the stinkbug sprays it in It's Tough to be a Bug) is often regarded by many as 5-D. However, since there is no standard for using these terms, each company uses its own terminology and it is often confusing. It is important to disregard the marketing slogans (4-5-6-7D) used by different companies and to check what is exactly offered for both the visual and sensory experience.