Iris
Iris explained in an easy to understand way:
Imagine trying to watch a movie on your phone outside on a sunny day. Just like you adjust the brightness settings on your phone to make the screen visible, the iris in your eye adjusts to control the amount of light that enters. The iris is like the phone's brightness control, expanding or contracting to let in just the right amount of light so you can see clearly, whether it's bright or dim around you.
Practice Version
Iris: The colored part of the eye, it controls how much light enters the eye. Iris. The iris is a ring-shaped tissue that adjusts the size of the pupil to regulate the amount of light entering the eye.