GGR (gross gaming revenue) is the operator’s revenue before costs: what players staked minus what they won. It is where the calculation starts, but in most programmes it is not the base for commission.
Example. The affiliate’s players stake 40,000 EUR in a month and win 34,000 EUR. GGR is 6,000 EUR. The programme deducts bonuses, taxes and fees from it to get NGR, and applies the RevShare rate to that.
When a programme advertises “RevShare up to X%”, always check whether the percentage applies to GGR or NGR. The same rate on GGR and on NGR gives very different commission.