Scouting radius
How far you are able to see into the shroud. Heroes usually have a scouting range of 5, though it can be increased by Scouting and/or equipping the Spyglass and/or Speculum.
Having a high scouting range is usually not that good. It can help a bit in the early game, but unless there are a lot of Necropolises with Covers of Darkness built, the advantage will be quickly lost.