The Backlink Gap tool analyzes your competitors referring domains to find the backlinks for which they are ranking but that you don’t.
In other words, as the names states, it finds the gap between your backlinks and those of your competitors.
This helps you discover where your competitors are getting their backlinks from so you can try to get some yourself.
Once you identify the backlinks you don’t have, you can add the referring domains to your backlinks planner so you can work on getting them later on.