The demand for a good or service is the amount that consumers are willing to buy at given prices over a period of time.
Demand for a product shows us the relationship between its price and the quantity which will be bought by consumers. Economic theory shows us that as the price increases for any good or service, the quantity demanded for that good should decrease. This is commonly referred to as the law of demand.
The opposite also holds true: as the price of a good or service decreases, the quantity demanded should increase.
Demand is a key concept in economics as understanding the demand of consumers is important for firms and governments to ensure money is being spent and circulating throughout the economy.