Consumer Surplus
Plain definition
Consumer surplus is the difference between what buyers were willing to pay and what they actually pay. Graphically it is the area below the demand curve and above the market price, up to the quantity traded — a measure of the net gain buyers get from participating in the market.
In economics
Consumer surplus is welfare economics' core measure of buyer benefit. Policies are judged partly by how much consumer surplus they create or destroy: a price fall transfers surplus from sellers to buyers and creates new surplus, while a tax shrinks total surplus and leaves part of it as deadweight loss.
Example
You would have paid up to 500 rupees for a novel but buy it for 300 — your consumer surplus is 200 rupees. Across all buyers, if 1,000 readers each valued the book above 300 rupees by an average of 150, total consumer surplus is 150,000 rupees.
Consumer surplus is often mistaken for money buyers literally hold or save. It is not cash in hand — it is the extra value buyers receive beyond what they paid, much of it psychological. Nobody collects their consumer surplus; it simply measures how much better off the purchase made them than the next-best use of the money.