Remnant inventory is usually defined as an ad inventory which is not sold directly by in house sales teams with guaranteed delivery. Remnant inventory is due to excess supply and ad inventory forecasting difficulties.
Remnant inventory is sold off at wholesale prices to a large range of ad networks. These large networks resell this inventory to advertisers on a CPM, CPC or CPA basis. Remnant inventory can also be sold through RTB and ad exchanges.
Remnant inventory is often sold through blindbuy.
Remnant inventory is not necessarily low quality inventory since unsold initially premium inventory can become remnant inventory.
Remnant inventory selling prices may be very low and sometimes well below 1$ CPM.
For publishers, the validity of selling remnant inventory is a matter of debate. Some consider that selling remnant inventory at very low price is shooting oneself in the foot in regards of overall inventory value and some big publishers have officially stopped to sell remnant inventory through ad networks or public ad exchanges.
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