A small addition: Structural typing means that TypeScript normally allows extra properties, but in contexts where you're immediately declaring and using a type, TypeScript will complain.

For example: `const user = { name: 'Bob', city: 'Reykjavík' }; saveUser(user)` is allowed because of structural typing. But `const user: User = { name: 'Bob', city: 'Reykjavík' }` throws a compile error; you're telling that you're specifying a `User`, but the value you give is not (just) a `User`.