In the world of search, conversions occur when users perform a query and click on a result from the SERP. Higher quality search engines will have a higher conversion rate than lower quality search engines, because a higher conversion rate indicates that users are clicking on results more often and therefore finding more relevant results for their queries. Conversion rates can be compared alongside exit rates, which indicate when a user performs a search then immediately exits the SERP without clicking.
Note: this is a different usage than most ecommerce professionals are accustomed to, since in ecommerce the word conversion generally refers to a series of actions that conclude with a customer completing a transaction. That being said, Swiftype ecommerce customers have observed that after implementing Swiftype, users who begin shopping with search are up to 5x more likely to complete a transaction.
Swiftype users can track conversion rates by integrating Swiftype with Google Analytics.