¿Qué es lo que retorna un objeto Callable al ser ejecutado por un ExecutorService?

public class SumaCallable implements Callable<Integer> {
    private final int a;
    private final int b;
    public SumaCallable(int a, int b) {
        this.a = a;
        this.b = b;
    }
    @Override
    public Integer call() throws Exception {
        return a + b;
    }
}
ExecutorService executorService = Executors.newSingleThreadExecutor();
SumaCallable sumaCallable = new SumaCallable(2, 3);
Future<Integer> resultado = executorService.submit(sumaCallable);
executorService.shutdown();