Teen Gothic

I guess most goths concider goth and i do too. but sometimes i see people here and there claiming they are not goth. i don't realy get it even if they're not under this label they're still post-punk which is super close and i know not all post-punk is goth but they're definetly are. what funny is i heard someone say "just beacuse they had sad lyrics dosn't mean they are goth". so what actually make a band sound goth than ? they had sad/melancholic lyrics and also gothic/darkwave-ish instrumental.