What is a Lens and what is the value of updated?

type Lens<S, A> = {
  get: (s: S) => A;
  set: (a: A, s: S) => S;
};

const nameLens: Lens<{ name: string; age: number }, string> = {
  get: (s) => s.name,
  set: (a, s) => ({ ...s, name: a }),
};

const user = { name: "Alice", age: 30 };
const updated = nameLens.set("Bob", user);