What exactly does the depth of field of a camera mean?

Simply put, the depth of field is the "acceptable clear area" before and after focusing on a clear focus. The characteristic of this distance is that the clear distance behind the real focus is longer than the clear distance in front. For any aperture, the depth of field behind the focus is about twice that before the focus. We generally call it depth of field (or short depth of field) if the clear distance before and after is short; Moreover, the range of clarity is large, which is generally called deep scene (or long depth of field).