Revenue or Income
Revenue (also called gross income) is the money a company receives in a given period from sales of its goods or services. It includes everything the customer pays the company for, including goods and shipping and handling. Note that sales tax is not included in revenue as it is not money due to the company.
A company's revenue is the sum of the revenues from the sale of all its products and services. For a product, revenue in a period equals the price of the good times the quantity of the good sold in that period. This is usually stated as "revenue = price x quantity". If a movie company sells one million DVDs a year at a price of $10 per DVD, the revenue from DVD sales is $10 million for that year.
Marginal Revenue
The revenue you get from selling one more item. In the DVD example the marginal revenue is $10.
Net Sales
Many retailers report revenue as "Net Sales" - that is, revenue from sales less returns.