Scarcity rents.
wSuppose now that the input suffices to produce QD.
$/Q
Q/t
MR
D
C
PA
QA
wA competitive industry would set price PD and scarce factor would earn  rent (PD – C)QD .
wBut a firm that controls all the factor would also want to restrict output to QB .
QD
PD
QB
PB
wThere is now deadweight loss.
wThe firm’s profit is now
(PB – C)QB .
The difference between the profit and the scarcity rent is the monopoly rent.
This analysis follows Winter (1995, pp. 159-167).