From what I understand in the references in the MM and PHB to Truesight, it seems that a creature with this sense can see into the Ethereal Plane and see invisible things/creatures. However, does this allow the creature to see through solid rock, e.g. if a PC was out of typical line of sight, with 100% cover, hiding behind a large tree or a stone pillar?
There was some confusion about this in a recent campaign. The way I would interpret it is that having Truesight does not allow a creature to see through objects, e.g. like x-ray vision. For me, seeing the "invisible" does not mean the same as seeing the "non visible".
I would appreciate any RAW answers using 5e literature and/or experience on applying a house-rule regarding this matter.