RTB is a means by which advertising inventory is bought and sold on a per-impression basis, via programmatic instantaneous auction, similar to financial markets. With real-time bidding, advertising buyers bid on an impression and, if the bid is won, the buyer’s ad is instantly displayed on the publisher’s site. Real-time bidding lets advertisers manage and optimise ads from multiple ad-networks by granting the user access to a multitude of different networks, allowing them to create and launch advertising campaigns, prioritise networks and allocate percentages of unsold inventory, known as backfill.