Successful Search Score
This column contains the percentage of searches that generated a click on one of the search results. That is, what percent of people that did that search for the same keyword, actually found and clicked on a result returned by the search engines.
The % is rather insightful as it provides a very clear indication on search terms that generate clicks.
It also provides a great way to find search terms that are currently not optimized for. If the results returned do not generate clicks, then obviously vast majority of users do not see any relevant results, so spending time optimizing on these low Successful Search Score terms could be a valuable exercise.
And finally it also highlights search terms that have very high Successful Search Score percentages as ones that will be optimized and will be harder to compete against. So closers to 100% will mean that users tend to find what they are looking for in the results returned by the search engines.