Do you mean ROI?
It stands for Return on Investment. It means the money you winnings compared to the buyins.
It's calculated as
the money won - buy-in /buy-in and is a percentage value.
If your ROI is high, it means you're a profitable player. If it's negative, it means you're loosing money in the long run.
The ROI is calculated for each game and then as an average over all games.
For example if you win 4$ in an MTT with a 2$ buy-in, your ROI = (4-2)/2= 100%
If you do not cash in in the next 2$ MTT, the ROI is (0-2)/2= -100%.
Total ROI= 100%+(-100%) = 0%.
Your wins are 2$ from first MTT and -2$ from second MTT = 0$.
So it shows you did not win or loose any amount.
Hope that helps.