What is the foreground and background? What is the front and back diameter in photography? Can you give me an example?

For example, in the photo of lotus, in order to highlight the main body, the photographer blurred the foreground. The lotus leaf in this picture is the foreground. If a painting has a three-dimensional sense and a sense of hierarchy, it must reflect the front and back, that is, the front and back scenery. Even in the picture, there is something in front and something in the back, which is not empty. It couldn't be more popular, haha.