Consolidator

An airline consolidator, also known as a bucketshop, is a business that buys tickets in bulk (at deep discounts but with many restrictions) from airlines and resells them to travel agencies. Consolidators are wholesalers and are prohibited (by contract) to deal directly with the public, so these tickets must be obtained through a retailer. Major travel sites such as Orbitz, Expedia, Travelocity, nor aggregators such as Kayak.com, SideStep, Farecast do not show fares that are originated by a consolidator. It is more common for U.S.-based consolidators deal with flights involving an international destination rather than with domestic flights.

From http://en.wikipedia.org/