A pupil is the black opening in the middle of the colored part of your eye (iris). It is responsible for controlling the amount of light that enters your eye. Muscles in the iris contract or dilate the pupil, making it smaller or larger to adjust to different lighting conditions.
For example, when you walk into a dark room, your pupils will dilate to let in more light, and when you are in bright sunlight, they will constrict to protect your eyes. This process helps you see clearly in a variety of lighting situations.
