What do economists mean by a price floor?

Answer:
A price floor is a minimum price set above the equilibrium price. The price floor can take the form of a government policy under which the government will not let the price fall. Such a policy has been introduced by Canadian governments to support farmers in their production of dairy products, hogs, and poultry, for example.

The government, usually at the federal level in Canada, establishes a minimum price, and then buys any surplus output at that price. O'Sullivan, in Microeconomics: Principles and Tools, suggests that previous to the policy, price will have been just high enough to cover all the farmers' costs. But a price floor allows farmers to earn a surplus, and with an increased price, farmers have an incentive to produce more of the good. The market will move up along the supply curve and away from market equilibrium. Spillovers are costs or benefits from a good, experienced by people who did not decide how much of the good or service to produce or consume. A competitive market is efficient in the sense that it has no spillover costs or benefits. The price floor provides spillover benefits to farmers and levies spillover costs on consumers of the agricultural product. Consumers lose whatever extra they are paying over and above the equilibrium price.

(Source for examples: Art O'Sullivan, Shefrin, Moir, Microeconomics: Principles and Tools, First Canadian Edition, Toronto: Pearson Education Canada, 2001, pp. 108-117.)