The Similar Searches widget returns searches that have been run in the past which are similar to the currently executed search. This takes into account semantic similarity of the terms.
It is a great aid for users to expand on which other queries may help them get to their results.
This functionality depends on Activity Tracking having been set up, as the data is collected from the activity tracking project.
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This page can now be found at Similar Searches Widget on the Squirro Docs site.