What are higher-order types in TypeScript?

Higher-order types are types that take other types as arguments and/or return types — analogous to higher-order functions in functional programming. All generic utility types are higher-order: Partial<T>, Record<K, V>, etc. You can compose them: type PartialRecord<K extends keyof any, V> = Partial<Record<K, V>>;. Type-level functions: mapped types and conditional types act as type-level functions. A generic mapped type like type Stringify<T> = { [K in keyof T]: string } is a type-level function that takes T and returns a new type. You can create complex type transformations by composing these: type MakeGetters<T> = { [K in keyof T as `get\${Capitalize<string & K>}`]: () => T[K] };. Higher-order types enable powerful meta-programming in TypeScript — building type-safe APIs, ORMs, validation libraries, and framework integrations that would be impossible with simple type annotations.