In economic terms, what is supply?
The definition you give here is not quite right. What you are describing is the quantity supplied.
The supply of a product is the amount of that product that suppliers are willing and able to produce at every price point. In other words, supply is a relationship between price and quantity and is represented graphically by a line, not by a single point. The law of supply states that there is a direct relationship between price and quantity supplied. That is, (all other things being equal) producers will be willing and able to produce more of a product as the price of the product (that they get when they sell it) rises.