The total dollar value of merchandise sold over a given period through a customer-to-customer or e-commerce marketplace.
Why it matters: GMV measures the scale and throughput of a marketplace, but it is NOT revenue. Revenue is only the take rate (commission) the marketplace keeps.
In practice: If eBay facilitates the sale of a $100 item and takes a 10% fee, the GMV is $100, but eBay's revenue is only $10.