What is the concept of "distortion" in photography?

Hello, it seems that when the lens is imaging, the magnification of the image formed in different areas of the field of view is different. This is a kind of distortion, and the closer it is to the edge of the picture, the more serious it is. \x0d\ Barrel distortion (negative distortion): the straight line of the image except the central cross line bends inward \x0d\ Cushion distortion (pincushion distortion): the straight line of the image except the central cross line bends outward \x0d\ distortion only causes the image to be distorted and not as clear as the image.