A discriminator is like a guard that checks if something is allowed to go through or not. Just like how your parents might check if someone is allowed to come into your home or if a toy is safe for you to play with. The discriminator checks some information about a thing, like a document or a person's skin color, and decides if it's okay or not.
Okay, let's say you have a box with different colored marbles in it. And you want to only pick out the blue marbles. You use a discriminator which is like a little tool that helps you identify which ones are blue and which ones are not. It might be like a little flashlight that helps you see the color better!
In other contexts, a discriminator can also help with things like making sure people have the right credentials to enter a building, or checking if someone is old enough to watch a certain movie. The discriminator asks some questions and based on the answers, it decides if the person can go forward or not.
So, think of the discriminator like a guard that makes sure everything is good and safe before letting it pass.