I did a search and found this which I suspect is what they are referring to.

You gain the ability to see into the hidden layers of reality, revealing eldritch traces and secrets. For the duration, you gain advantage on Intelligence (Arcana) and Wisdom (Insight) checks.

Additionally, you can see creatures that are invisible, ethereal, or otherwise hidden within 60 feet of you, though you can’t perceive exact details. Creatures detected in this way appear as faint, shadowy figures in your vision.