What is Real volume?

Real volume is the actual number of contracts traded, as reported by the exchange. In GC, every trade is published with its price, its size (say, 3 contracts) and its time. CME's market-data feed even identifies which side was the aggressor (Chapter 3 explains how). Because all GC trades pass through one central order book on CME Globex, the exchange's count is the complete count for that contract.