What does "Drain energy" actually do?

[Vectros]

I see a high level ability with this property, but don't see anywhere in the tutorial that explains this. I'd guess it's like a life drain AOE effect, or life steal, but not too sure...and just how much of it is there?

[DreamSword]

It restores some of your HP when you damage enemies. The drain itself isn't alot, but it helps.