The difference between a revenue and payout is how much you are receiving for a successful conversion for an offer as opposed to how much you are paying out to your publishers. 

For example: if you earn $2 every time a user makes a purchase this is your revenue and if you payout $1 to your publisher for their role in acquiring the user its your payout. Thus by deducting the Revenue and Payout ($2 -$1) you get your profit $1.