Medusa and Umber Hulk and probably a number of other monsters suggest that a target can avert its eyes to avoid its effects.
For example, the medusa's Petrifying Gaze:
Unless surprised, a creature can avert its eyes to avoid the saving throw at the start of its turn. If the creature does so, it can't see the medusa until the start of its next turn, when it can avert its eyes again. If the creature looks at the medusa in the meantime, it must immediately make the save.
I've scoured the books but I can't find what it means mechanically to avert one's eyes. I'm assuming it's related to partial blindness or concealment but I'm not sure. So what are all the things that happen when your eyes are averted? Can you cite the rules so that I can understand it as thoroughly as possible?
Best Answer
Averting your eyes does exactly what it says it does: You willingly look away from your target.
When you cannot see a target, you have disadvantage on attack rolls made against it (PHB p. 183) and many spells that require sight of a target will not work. If a spell indicates it affects a target that you can see, then it will not work if you avert your eyes. It's worth noting that averting one's eyes is not a common interaction in the game.
No, you cannot look at the floor and retain vision of her. If you avert your eyes, you cannot see her. If you choose not to avert your eyes, you might get turned to stone
Also, if you cannot see the medusa, she has advantage on attacks against you. PHB p. 195 :
The same goes for monsters against you.