Basics · also called remnant, unsold inventory
Remnant inventory
Remnant inventory is ad space a publisher has not sold through direct deals, which is then offered through programmatic channels, networks or house ads, usually at lower prices.
Remnant inventory is what is left after the publisher's direct sales team has sold what it can. Rather than leave those slots empty, the publisher passes them to SSPs, exchanges or ad networks, or fills them with house ads promoting its own products.
In the early 2010s, real-time bidding was widely seen as a way to sell remnant cheaply. The term now sounds dated because programmatic channels often compete directly with direct sales in a unified auction and can pay more than direct campaigns for a particular impression. Many publishers prefer phrases like "non-guaranteed" or "open auction" inventory.
The term still matters for understanding prices. Remnant sales tend to have lower CPMs and less information about who is buying, which is one reason buyers use PMPs and curation to find quality supply, and why fraudsters target remnant pipelines through traffic arbitrage and domain spoofing.
Think of it like this
Remnant inventory is like end-of-day bakery bread: still good, sold at a discount because it did not sell at full price earlier.
An example
A sports site sells 60% of its 10 million monthly impressions directly at US$15 CPM; the remaining 4 million go to the open auction at an average US$2 CPM.
Related terms
Direct-sold advertising
Direct-sold advertising is ad space sold by a publisher straight to an advertiser or agency through a negotiated deal, usually with a fixed price and guaranteed volume.
Open auction
An open auction is a real-time programmatic auction in which any approved buyer connected to an exchange can bid on a publisher's impressions, without a pre-arranged deal.
Fill rate
Fill rate is the percentage of ad requests that are actually filled with an ad, calculated as impressions served divided by ad requests, multiplied by 100.
Ad network
An ad network is a company that aggregates ad space from many publishers and resells it to advertisers, usually in packaged bundles and often with its own pricing and targeting.
Sell-through rate
Sell-through rate is the percentage of a publisher's available inventory that has been sold, usually through direct or guaranteed deals, over a given period.