Search Monetization or Search Feed Monetization is a monetization method where individuals/affiliates/businesses generate revenue through the use of SERP (Search Engine Results Pages) and Search Feeds (Yahoo!, Bing, etc.).
Besides this, this type of monetization includes displaying sponsored units or content with the search results on the side. This also offers paid search listings and this advertising space is being sold on searhc engine results pages.
Basically, you are making money from the clicks on search pages which contain relevant ads matching the keyword they end user ia searching for. The revenue depends on the quality of advertising and the user experience. For example, there are keywords which are higher in demand and that generate more revenue. The other factor is the popularity of the search feed or engine.