After image is the term used for the image that persists in the eye even after the original image that the eye was being exposed to is removed.
After image is a type of an optical illusion and can either be a positive or a negative after image.
If the colors of the original image is retained in the after image then this is termed as positive after image.
If the colors of the original image are reversed in the after image then this is termed as negative after image.
After image can occur either due to a prolonged exposure to a very bright light against a dark background such as headlights or after a prolonged exposure to a colored image.
One way in which classification is used at school is the separation of different subjects and subject materials. For instance one day you may go to a math class, while another day you may go to a french class.
