What do you mean by 24 frames per second in the movie?

24 frames per second in a movie is the speed of the movie.

Film speed refers to the speed of film rotation in a movie camera, which is usually calculated in fps. The normal shooting speed is 1.24 fps. The standard projection speed is 24 fps.

Extended data:

There are also three kinds of rotational speeds: in Europe, the electrical frequency is 50Hz, which is 25fps to match the video signal; Silent 16 cm film is18 fps; Some 8 cm is also 18fps.

Unless it is necessary to use 25fps, it is best to set the rotation speed to 24fps, because that is the standard rotation speed of the sound film and applies to all peripheral devices. Only when the speed of the camera is consistent with the speed of the projector, the action on the screen is natural and normal.

Baidu encyclopedia-movie speed