Generalized algebraic data type

Generalized algebraic data types (GADTs) are a way of writing types in a programming language. Think of a type like a way of organizing information into different categories. GADTs are special because they let you make different types for different cases. For example, consider a type called Animal. With GADTs, you could create different types for different kinds of animals like Dogs, Cats, and Birds. Each one of these would have different kinds of information (like dog breeds, or bird colors) but could all be grouped together as different types of Animals.