If it is anything, "small talk" is talk that you don't mind other people hearing and joining. And if you think about that at a distance, it makes it very big talk indeed.
To me, "small talk" is mundane chit-chat that you do mostly to be polite or to break the ice. "Hi <neighbour>, weathers been awfully cold lately hasn't it? Yes, can't wait till summer. Did you watch the game yesterday? Anyway catch you later!" kind of things.
But it's not small if that is the conversation that allows someone you both haven't yet met to feel at ease in joining in to chat with you. That makes it powerful, because it leads on to people introducing themselves, more common ground being found, etc.
Also, it might be the only kind of talk that can "break the ice" in the general case. I mean -- imagine replacing small talk with a deep question about politics or science or music theory. It couldn't work so well in general.
That is what I mean about its significance. Almost all of us exist solely because of small talk between our until-then-unknown-to-each-other parents, for example.
"Small" talk is the beginning of almost everything.
I see what you're saying. I agree, if it helps break the ice or is the "introduction" for further conversation, then it serves an important purpose. Even in the case of maintaining some kind of friendliness with a neighbour, that serves a purpose too, I suppose.
All talk is significant.
If it is anything, "small talk" is talk that you don't mind other people hearing and joining. And if you think about that at a distance, it makes it very big talk indeed.