"Raw" sales income; the amount customers actually pay the company when they make their purchases.
When a company sells products, it has to make allowances for some portion of its sales for products expected to be returned, lost in delivery, or otherwise requiring the company to refund the customers' money.
The "official" revenue number, known as sales revenue,
equals gross revenue minus these allowances.
Gross revenue is generally not an interesting number for investors.
One case where it is interesting is when you're tracking the progress of a startup company.
It's possible that at the very beginning they'll be doing such a tiny amount of business that actual sales will be less than the allowances for refunds,
meaning that sales revenue will technically be a negative number.
In this case the company will issue news releases about its gross revenue,
so investors will at least know that a few customers have been showing up and laying out some cash.