The amount of a product people are willing to buy at a certain price is called Demand.
The law of demand assumes all other factors to remain equal except price of a commodity. It says that if all other factors remain equal, the higher the price of a good, the less people will demand that good.
In other words, Law of Demand states that if the price of a commodity increase, the demand of that commodity will decrease. If the price decreases the demand will increase.