Short for “return on investment,” in poker the term is most often used with reference to tournaments as a way to measure and compare players’ profitability.

ROI is calculated as a percentage by dividing one’s profit (the amount one cashes for minus the buy-in) by one's expense (the buy-in) and multiplying the result by 100. Say a player enters a $100 tournament and cashes for $150. Divide the profit ($50) by the buy-in ($100) to get 0.5, then multiply that by 100 for an ROI of 50%.