What is meant by "marginal disutility of labor" in Keynes General Theory

Question

Sorry for the newby question, started reading Keynes general theory (1936) and am confused by this paragraph in Chapter 2:

The traditional theory maintains, in short, that the wage bargains between the entrepreneurs and the workers determine the real wage; so that, assuming free competition amongst workers, the latter can, if they wish, bring their real wages into conformity with the marginal disutility of the amount of employment offered by the employers at that wage. If this is not true, then there is no longer any reason to expect a tendency toward equality between the real wage and the marginal disutility of labor.

My understanding is that "marginal disutility of labor" refers to (mental or physical) adverse effects of each additional time-unit of labor expended. Is this correct? What would it mean then to say marginal disutility of labor is equal to the real wage?

Answer 1

My understanding is that "marginal disutility of labor" refers to (mental or physical) adverse effects of each additional time-unit of labor expended. Is this correct?

Yes this is correct.

What would it mean then to say marginal disutility of labor is equal to the real wage?

It means that in this scenario real wage is exactly as high as needed for the person to provide the labor they provide on margin. If real wage would be lower than marginal disutility of labor a person would provide less labor on margin. If real wage is higher than marginal disutility of labor a person would likely seek to increase their working hours. If they are equal you are in some sort of stable equilibrium where person, on margin, is content with their current labor supply.