What does the depth of field mean in photography? It's especially nice to look at the works taken with large depth of field.

Depth of field means the clear range of the photo. Usually, people are clear when the background is blurred before and after portrait shooting, and the scenery before and after is clear. This is the depth of field, controlled by the photographer (clear range). Simply put, the photographer controls the audience's line of sight and looks wherever he wants. This is the depth of field.