This metric is calculated by dividing the participated revenue by the suggested paid media spend. The outcome of this is a target ROAS, for you to compare to its current ROAS. The current ROAS should at the least be equal to the target ROAS for the respective traffic source to be profitable.
N.b.: please take the incrementality index into account when interpreting target ROAS, for it also requires other traffic sources to achieve the participated revenue.