Originally Posted by What is 4D?

A 4-D film (sometimes written 4D film) is a marketing term that describes an entertainment presentation system combining a 3-D film with physical effects in the theater, which occur in synchronization with the film. Because the physical effects are expensive to set up, 4-D films are currently presented only at special venues such as theme parks and amusement parks.

Some of the effects simulated in 4-D films include rain, wind, 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.