Bullet Time: It is a special and visual effect technique in which a row of still cameras are used to capture the scene. They are activated either simultaneously or with a phase lag. Later these frames are digitally assembled together to produce an effect of changing the view point of the audience in an orbit going around the scene. Bullet time is a trademark of Warner Bros. This technique although had been in existence for a long time, it was popularized by the film The Matrix released in 1999. One of the unique points of the film was to show bullet time visuals of the actions happening inside the Matrix. In particular the scene in which Neo escapes the stream of bullets fired towards him had been very popular.

The technique although dates back to the 19th century even before cinema. The Californian governor had engaged in a debate on if all the legs of the horse is in the air when it gallops. To settle this Eadweard Muybridge had done some experiment with still cameras taking the picture of galloping horse by arranging the cameras along the race track  and each camera was actuated by a taut string stretched across the track; as the horse galloped past, the camera shutters snapped, taking one frame at a time. He then arranged the photographs in on a glass disk and spun it in front of a light source. Could this have been the inspiration for Thomal Alva Edison to invent motion pictures?

Now this technique is being used in Free viewpoint Television (FTV)  in filming live shows.  At the time of The Matrix FTV was not mature… the filmmakers still did an wonderful job of creating a whole new experience.

Source: Wikipedia