What is a type alias in Kotlin?

A type alias provides an alternative name for an existing type without creating a new type. Declared with typealias: typealias UserMap = Map<String, User>. The alias and the original type are fully interchangeable at compile time — the compiler replaces the alias with the actual type. Type aliases are most useful for shortening complex generic types, naming function types for clarity (typealias Callback = (Result<Data>) -> Unit), and giving meaningful names to platform types. Unlike value classes (inline classes), type aliases have zero runtime overhead but also provide no type safety between the alias and the original.