Monopsony is the analogue of a monopoly, this time with market concentration on the demand side.
In a market with is a single buyer, the competitive pressure that drives price up to the efficient level is absent. The monopsonist will be able to set a price that maximizes total consumer surplus. [See also: Labor market monopsony]
You can try varying price in the first graph (on the left) to see how consumer surplus varies. On the right side, you can see the optimal monopsony pricing level.