What does it mean to blur the picture?

When a camera is shooting, it has a focusing process. Under normal circumstances, the image is clear where the focus is. At the same time, before and after the focal length of the lens, there is a so-called depth of field, which is the range from focus to blur in popular parlance.

the larger the aperture of the lens, the smaller the depth of field. On the contrary, the bigger.

Take the picture below as an example. The focus is on the flowers, so the flowers are clear. Because of the large aperture and small depth of field, the picture before and after the flower, that is, outside the focus, is blurred. This kind of fuzziness is intentional, which makes the audience's attention focus on flowers. This kind of treatment is generally called blurring.