Which amongst desire, surplus, ability, willingness is not a component of demand?

Surplus occurs for a consumer when the difference in the price a consumer set aside or is willing to pay for a particular commodity is higher than the actual price of that commodity. It also occur for a producer when the amount a producer gain from selling a commodity at a higher price is more than the initial price of the commodity that the producer was willing to sell.

Desire is commodity you wish to have, regardless of your purchasing power, needs and wants. It is a component of demand. Ability is also a component of demand; it is the financial power of a consumer to purchase goods or services. The willingness of consumers to buy a good or service is a key component in demand.