$E^a$ Demand is best described as

the total satisfaction that consuming a good provides people at different prices.

the quantity of a good or service that consumers will substitute when the price of a good changes.

the quantity of a good or a service that people are willing and able to purchase at different possible prices. the additional satisfaction derived from a quantity of goods and services obtained when income increases. the quantity of a good or a service that people will offer for sale at different possible prices.

The law of demand says that

as the price of a good increases, buyers are willing and able to purchase less.

as the price of a good decreases, buyers are willing and able to purchase less. higher prices cause buyers to demand more.

buyers demand lower prices.

higher prices cause less demand.