from
The Collaborative International Dictionary of English v.0.48
Consumer's surplus \Consumer's surplus\ (Polit. econ.)
The excess that a purchaser would be willing to pay for a
commodity over that he does pay, rather than go without the
commodity; -- called also
{consumer's rent}.
The price which a person pays for a thing can never
exceed, and seldom comes up to, that which he would
be willing to pay rather than go without it. . . .
The excess of the price which he would be willing to
pay rather than go without it, over that which he
actually does pay, is the economic measure of this
surplus satisfaction. It has some analogies to a
rent; but is perhaps best called simply consumer's
surplus. --Alfred
Marshall.
[Webster 1913 Suppl.]