Hello!
ROI>100% happens when your net profit is higher than the initial investment.
Let's say you bought 10 apples for $100 (or $10/apple). This $100 is your 'cost of investment'. Let's then say that you went and sold these apples in a place where they were very highly valued. You managed to get $100/apple, for a total sales value of $1,000. Let's assume that, after you cover transportation costs, renting a space to sell them, etc., you have $200 left (your net profit). Your ROI is 200% ($200/$100). 200% ROI means you made back 100% of your initial investment of $100, plus another 100%.
This is an exaggerated example, but hopefully it helps highlight the concept of ROI>100%.
Best,
Maria