What is the flatMap operation called in the context of monads?

type Result<T, E> =
  | { ok: true; value: T }
  | { ok: false; error: E };

const flatMap = <T, E, U>(
  result: Result<T, E>,
  fn: (value: T) => Result<U, E>
): Result<U, E> =>
  result.ok ? fn(result.value) : result;

const parse = (s: string): Result<number, string> => {
  const n = Number(s);
  return isNaN(n)
    ? { ok: false, error: "Not a number" }
    : { ok: true, value: n };
};