Final answer:
The term for the adjustment in the amount of a good that buyers are willing and able to purchase in response to a price change is known as 'change in the quantity demanded', rooted in the principle of the law of demand.
Step-by-step explanation:
The change in the quantity of a good, service, or resource that consumers, firms, and governments are willing and able to buy due to a change in its price is called the change in the quantity demanded. This is described by the law of demand, which states that there is an inverse relationship between the price of a good or service and the quantity demanded. When prices rise, the quantity demanded generally falls, and when prices decrease, consumers are typically willing to buy more, thereby increasing the quantity demanded. This principle assumes that all other variables that affect demand are held constant.