When 30-year old man says “It’s meta,” what does it mean? In what situation and of what sort of object they use this phrase?
Something is meta (and self referential) if it is about itself. (Strictly speaking, you can be meta by being about the thing's own category, rather than this specific individual thing, but the key is "about".) If you substitute the word "about" where you see meta in a sentence longer than "it's meta", you will get close to the meaning, even though the sentence you make won't necessarily be grammatically correct. Some examples of meta things: In my experience, Kids These Days call things meta if they are truly meta (arguing about the argument), or off topic, or just not what they wanted to talk about. Some of them love the self-referential thrill of meta (my youngest once used the new label maker we bought to make a label that said label maker and stuck it onto the label maker with delight), but most don't and think it's something to be avoided. Your kids may vary.