Definition of Marginal Revenue

marginal revenue is the change in total revenue that is obtained by selling an additional unit of the commodity.
What is revenue in economics?
Revenue is amount earned by the producer by selling the output produced by him.
How to calculate marginal revenue?
Marginal revenue is calculated by dividing the change in total revenue (?TR) by change in quantity (?Q) or as the difference between Total Revenue of n units of output (TRn) and TR of n-1 units of output (TRn-1)