It's "Fleet Range." At the top level, you see the total fuel in your fleet and the distance of all move orders. However, the information that's missing is the overall range the fleet could travel. To find this out, you currently have to expand the ship tree and check the range of each individual ship.
Admittedly, one reason for this might be the ability to transfer fuel within the fleet. But without considering fuel transfer, the current interface requires constant checking of individual ships to get an idea of the fleet's range.