Initially, moving pictures meant only the movement that is perceived when a string of celluloid - recorded images are projected at a rate of 16 or more frames per second (see persistence of vision). Today, motion pictures (or "movies") are an art form, as well as one of the most popular forms of entertainment.
A feature film is usually defined as being more than 60 minutes in length.

Originally moving picture film was shot at a nominal 16 frames per second, but was changed to 24 frames per second with the introduction of sound. Other improvements since the late 1800s include the mechanization of cameras, allowing them to record at a consistent speed, the invention of more sophisticated film stocks, allowing directors to film in increasingly dim conditions, and the development of synch sound - , allowing sound to be recorded at the same speed as its corresponding video. Since the advent of many other media technologies, film may include a broad range of media - - both linear and non - linear, dramatic and informational, motion and still (though progressive).