Market failure means that

A) the law of supply and demand has stopped functioning.
B) our resources are not allocated efficiently.
C) the stock market has crashed.
D) prices are no longer reliable indicators of how much things cost.

Market failure occurs when the allocation of resources by the free market is inefficient, resulting in either a surplus of goods or services, or a lack of goods and services being produced. This can happen due to externalities (when the actions of one party affect the well-being of others), monopolies, asymmetry of information, and other factors. The law of supply and demand still functions, but it may not lead to an optimal outcome. The stock market crashing and prices not being reliable indicators of cost are not necessarily indicators of market failure.