What does "depth of field" mean in photography?

Depth of field refers to the distance range of an object measured along the axis of an imager, which can obtain a clear image in front of a camera lens or other imager. That is, before and after the subject (focus), the image still has a clear range, which is the depth of field. In other words, the depth of field before and after the subject and the blur of the image presented on the surface of the negative are within the allowable dispersion circle.