A way to express confusion over a situation or an object... can be followed by the thing that is confusing, or just said by itself, usually with "this" at the end.
Mom: What even is this, Jacob? -points to line of powder on his desk.
or
Madison: What the fuck Alex? You're cheating on me?!?!? What even is this?!?!?
Nothing is non existent because if nothing was real then it wouldn't be nothing. But, "Nothing", used as a pronoun subject, is the absence of a something or particular thing that one might expect or desire to be present or the inactivity of a thing or things that are usually or could be active.
Being defined... "Nothing", used as a pronoun subject, is the absence of a something or particular thing that one might expect or desire to be present or the inactivity of a thing or things that are usually or could be active.