ROIROI stands for "Return on Investment" and in poker it gets used to measure the profits of a tournament player.
This is how to calculate the ROI:
For example: Hero expects to win $100 in a tournament and pays $50 +
$5 to take part. Hence the profit is:
ROI = (100 * ($100 - $50 - $5) / ($50 + $5)) = 81%