Remnant inventory is a term used in the context of online advertising to refer to ad inventory that has not been sold or reserved through a preferred or guaranteed deal, and is available for purchase on a first-come, first-served basis. Remnant inventory can include ad impressions that are unsold, unbooked, or under-delivering, and can be sold at a lower price than premium or guaranteed inventory. Remnant inventory can be an effective way for advertisers to access high-quality and high-performing ad inventory at a lower cost, and can help to maximize the reach and effectiveness of an advertising campaign. Remnant inventory can also be beneficial for publishers and platforms, as it can provide a way to monetize their ad inventory, and can help to generate additional revenue and profits. Remnant inventory can be an important part of an advertiser's media planning and buying strategy, as it can provide access to a wide range of ad inventory, and can help to optimize and maximize the performance of an advertising campaign.