The lease rate is indeed the rate used by a short-seller of the commodity to compensate the lender of the commodity for the lending. This definition provided by Student 3 is accurate. In commodity markets, a lease rate is a crucial concept that is often used in futures contracts. When a commodity is lent out, the lender is compensated by the borrower (the short-seller) at a certain rate, known as the lease rate. This rate is essentially the cost of borrowing the commodity. It is important to note that the lease rate is not a risk-free rate, nor is it used as an underlying asset on a futures contract. Instead, it is a cost that the short-seller incurs to borrow the commodity from the lender. This cost is necessary because the lender is giving up the opportunity to use or sell the commodity during the lending period. Therefore, the lease rate serves as a form of compensation for the lender's opportunity cost. In the context of financial assets, a similar concept exists where the short-seller compensates the owner for dividends. In the case of commodities, the short-seller may use the lease rate to make lease payments to the owner of the commodity. Therefore, the definition provided by Student 3 is the most accurate among the three.

Choice A is incorrect. The lease rate is not the risk-free rate at which a holder of a long position in the futures contract can finance his position. This definition confuses the lease rate with the cost of carry, which includes interest rates and storage costs among other factors.

Choice B is incorrect. The statement that 'lease rate is widely used as an underlying asset on a futures contract' is false.