Truesight

Source: D&D 5.2 SRD Rules Glossary

If you have Truesight, your vision is enhanced within a specified range. Within that range, your vision pierces through the following:

• Darkness. You can see in normal and magical Darkness.
• Invisibility. You see creatures and objects that have the Invisible condition.
• Visual Illusions. Visual illusions appear transparent to you, and you automatically succeed on saving throws against them.
• Transformations. You discern the true form of any creature or object you see that has been transformed by magic.
• Ethereal Plane. You see into the Ethereal Plane.