What is the pupil in human eye and what does it do?

The pupil is a dark, circular opening in the center of the iris (the colored part) of the eye. It allows light to enter the eye and reach the retina (the light-sensitive tissue at the back of the eye) to be focused into an image by the lens.

The size of the pupil is controlled by the iris, which contains muscles that can contract or relax to make the pupil larger or smaller. This adjusts the amount of light that enters the eye. In bright conditions, the pupil constricts (gets smaller) to reduce the amount of light entering the eye. In dark conditions, the pupil dilates (gets larger) to allow more light to enter.