Okay, so imagine you have a friend named Emily. Emily was born a boy, but she feels like she is really a girl. This is called being transgender. Some people might not understand or accept Emily for who she is, and might treat her unfairly just because she is transgender.
For example, Emily might want to go to a store and use the women's restroom, but some people might tell her she can't because she was born a boy. This is not fair. Or she might want to play on a sports team with other girls, but some people might say she can't because she used to be a boy, even though she identifies as a girl now.
Discrimination is when people are being treated unfairly because of who they are. It's like being picked on or bullied for something you can't control. Discrimination is never okay, and we should always treat people with kindness and respect no matter what.