GGR (Gross Gaming Revenue) is the gross gaming revenue: everything players wagered in a period minus everything they received back as winnings. It is the first line of any iGaming operations report.
It is important to understand what GGR is not. It does not deduct bonus cost, payment processing fees, game provider royalties or taxes on the activity. High GGR therefore does not mean a healthy operation, it only means volume of play with a house-favourable outcome.
In sportsbook, short-period GGR is heavily influenced by event results: a round of favourites winning drags GGR down without anything changing in the operation. In casino, GGR converges to the theoretical margin faster because the volume of rounds is far larger.
For business decisions the number that matters is usually NGR, which starts from GGR and deducts what actually left the cash box.