What does the column of digital camera mean?

Histogram is a distribution diagram that visually represents the exposure of all pixels. The leftmost side of the horizontal axis of the histogram represents extremely dark (dead black), the rightmost side represents extremely bright (dead white), and the middle represents the middle gray level. The vertical axis represents the number of pixels at a certain exposure brightness. Observe the histogram of the shot picture. If the whole picture is to the left, it means underexposure.

If the whole body is to the right, it means overexposure.