Alright kiddo, so do you know what a display is? It's when you show something to someone or something, like when you show your toy to a friend.
In zoology – that's the study of animals! – display means something very similar. It's when an animal shows off a certain behavior or feature to other animals.
For example, some male birds will do a fancy dance and show off their colorful feathers to attract a female bird. This is called a courtship display.
Another example is the threat display. Let's say you were a small animal and a big predator was coming toward you. You might make yourself look as big and scary as possible to try to scare the predator away. This is called a threat display.
So, in short, display in zoology just means when an animal is showing off something to other animals, either to attract a mate or to protect themselves. Cool, huh?