New Item: Death's Dance

I am confused as to what this item's primary unique passive means, exactly.

Dealing physical damage heals for 12% of the damage dealt. This is 33% as effective for Area of Effect damage.

It is the latter part which I am confused with. Does the term Area of Effect apply towards for example:

Tristana's E Explosive Charge Graves' Q End of the Line

Does it not apply to Ezreal's Q Mystic Shot (Unless Ezreal is equipped with Iceborn Gauntlet, is it applicable then?)

I would find an official Riot post about which abilities (If Area of Effect is even meant to be applied to abilities to begin with here) very helpful.

Or perhaps Area of Effect in the case of this items passive is meant as something else entirely that I'm missing.

Whatever the case, I feel that this term is very grey.

I would not feel confident buying this item on Corki for example because although I assume that Corki's Q, W, E, and R could all very well be potential candidates for this items passive, it's not exactly clear.

So to conclude, in a game where knowledge is as important as it is, I simply can't move myself to buy this item on my Graves without a more black and white description of the term Area of Effect and what it is being applied to here.

Even the League of Legends wikia isn't as insightful as I imagine it could be.

tl;dr What does Area of Effect actually mean in all of it's possible scenarios?