Cisnormativity is when people assume that everyone is either a boy or a girl and that their gender matches the sex they were assigned at birth (based on their body parts). It's like when someone thinks that if you have a penis, you must be a boy or if you have a vagina, you must be a girl. This kind of thinking forgets that some people might feel like their gender doesn't match what they were assigned at birth, or that some people might not feel like they fit into the categories of "boy" or "girl" at all. It's important to remember that there are lots of different ways to be a person and that everyone deserves to be accepted and respected for who they are.