Type theory

Type theory is a branch of mathematics that studies something called types. A type is like a category that things can fall into. Each type has a bunch of rules that objects must follow in order to fit into that type. Types help us to organize information, so that we can think about how things fit together. For example, if we want to talk about apples, we can assign a type called 'Fruit' to them. Apples would fit into that type because they are a type of Fruit.