Truesight was a type of magical sense that only a small number of creatures possessed, though powerful mages were able to access the ability through Spells. Creatures with truesight could, out to a specific range, see in both normal and magical darkness. In this range, they could see invisible creatures and objects, and automatically see through visual illusions and the forms of shapechangers.
Those with truesight could also see into the Ethereal Border wiithin the same range of their normal truesight abilities.