ROI
ROI is profit divided by total amount staked, expressed as a percentage.
In plain English
It measures return per unit risked rather than per bet, which is why it is comparable across people betting different amounts. Small ROI figures are normal and large sustained ones are rare.
Example
Staking 100 units in total and finishing 4 units ahead is a 4 percent ROI.
Why it matters
It is the standard way to compare betting performance, and the number most often quoted without its sample size.
How V8 uses this term
V8 publishes ROI alongside the number of settled picks it is based on, because the figure is close to meaningless without the denominator.