Items-for-query recommendations are based on how other users interacted with search results from the same query. This is one type of collaborative recommendation.
For example, if users have searched for "titanic" in the past and many of them clicked on the search result for the DVD of the movie Titanic (as opposed to books or memorabilia), then this method boosts the DVD item on subsequent searches for "titanic".
Below is an example of items-for-query recommendations based on a search for "madonna":
To use this type of boosting, signals must be enabled but recommendations need not be.