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.
person 1: hey
person 2: Hi!
person 1: What even is nothing
person2: uhh... I... whoah...what is nothing?
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.
Now you can answer...
What even is nothing?