What does it mean to empty the film in photography? How to avoid making a film empty?

When shooting people, still life or dynamic scenes, such as running people or cars walking in the street, we need to focus on the real point so that the viewfinder of the camera can clearly see the actual situation, or add a split lens to the viewfinder and press the shutter when the scene in the split lens circle is clear. If you shoot a dynamic scene, you need to turn on the autofocus servo of the camera, so you can shoot a clear picture. It should be noted that many SLR cameras now have a multi-point focusing system, which can set the focus off the center of the picture. If the scene in the center of the picture is not clear due to this setting, you need to turn off this function or focus on the center instead.