ROI - Return On Investment
For example with margin trading: you have $100 deposit. You using 10x leverage, open position on $100, and that mean you engage only $10 from your depo. In case price will go in right side (Up if you have Long, Down if Short), you will earn money. When cost of your whole position reach $110, it will mean that you earn $10, using only $10 of your depo, and in this case your ROI will be displayed like 100%.