An entity is a piece of information in an utterance that you want to extract. With the example “I want to order a pepperoni pizza”, you will have an intent “pizza_order”, since the user has the goal of ordering a pizza. But in this example the user also already informs us what kind of pizza they want, in this case a “pepperoni” pizza. The entity here is “pepperoni” since it is a piece of information regarding the sort of pizza that the user wants.