Search feeds · also called query, feed request, search request
Ad request
An ad request is a single call from a page to the search feed asking for ads to show for a particular keyword and visitor.
Each time a results page loads, it asks the feed for ads. That ask is an ad request. It carries the information the search engine needs to pick ads and account for them: the publisher's ID, the keyword or query, the Style ID, any Channel ID, language settings and, where required, fields such as referrerAdCreative.
The engine answers with zero or more ads. A request that returns at least one ad is "matched", and the share of requests that are matched is coverage. How many ads come back is governed by ad depth.
Requests are the top line of feed reporting. From requests flow matched requests, impressions, clicks and revenue, and ratios such as RPS are calculated against them.
They are also where quality control begins. Engines inspect requests for signs of automation or tampering, and Google's ad code by default sets a cookie used only for detecting invalid traffic on consented traffic. Sending requests that no real person triggered, or with altered keywords, is query fraud. Many feeds also limit the volume of requests a partner may send through a feed cap.
An example
For example, 1,000 visitors click a keyword, producing 1,000 ad requests. 900 return ads (90% coverage), and those pages produce 500 ad clicks.
Related terms
Coverage (ad coverage)
Coverage is the percentage of ad requests for which the search feed returns at least one ad.
Ad depth
Ad depth is the number of search ads returned and shown for a single request or results page.
Custom Search Ads (CSA)
Custom Search Ads is the Google AdSense code that lets a publisher request Google search ads for a query and display them on its own results page.
Channel ID (custom channel)
A channel ID is a label attached to search ad requests so that revenue and clicks can be reported separately for each page, campaign or traffic source.
Query fraud (fake search queries)
Query fraud is sending a search feed searches that no real person chose to make, in order to trigger valuable ads.
Feed cap (traffic cap)
A feed cap is a limit on how much traffic, how many requests or how much revenue a publisher may run through a search feed in a set period.
Sources: Google Developers: Custom Search Ads reference, Google Developers: Custom Search Ads web implementation