It averages out to medium talk.

If there's someone behind you, that's called "holding up the line."

Then you shouldn't be buying groceries to begin with, they should be getting them with their employee discount.

I would say that small talk is when you ask questions you don't actually care to know the answers to, just to fill the silence. "Did you catch the game last night?" is small talk if I'm talking to my coworker whose name I don't even remember, but it's not small talk when I'm talking to my friend who I know has been invested in the season, and whose opinion I actually want to know.

I didn’t say anything about not liking either of these. The two scenarios are qualitatively different. The purpose of the one at home is to learn what happened that day, how the other person feels about it, planning what we do with the rest of our day, and so on. It’s an exchange of information.
The purpose of asking the cashier about their day is not to actually learn what happened with them (unless you actually know the person of course). It is exchanging pleasantries or just making banter, without the intent of exchanging any information that matters to the other person. I don’t dislike it. But it’s not a conversation, it’s small talk.
I read your top level comment as well and you do seem really irked that some people differentiate small talk from conversation. It seems like you’re fighting windmills though, and it’s in fact you who for some reason has strong feelings about the topic.
Small talk is an important part of interpersonal communication, and it’s good when it creates a sense of comfort, belonging, or serves as the prelude for a deeper conversation. But it can be annoying if it’s self serving, because either it fails creating any positive feelings, or it never gets past the warmup phase. I don’t think there’s anything wrong with people who don’t enjoy small talk, or with those who do.

OP and all your down votes are from morons. Don't fret

There's a clear issue in how people define the phrase, and it's easy to understand why when I look up the definition and the Merriam-Webster defines it as "light or casual conversation" with the synonym of "chitchat" but the Cambridge dictionary specifically says that it's "conversations about things that are not important, often between people who do not know each other well."

Those are two very distinct views on the concept (with the second having a rather...negative connotation to it, in my opinion), and I think it gets even further muddled by one very simple thing that I think is the real root of the argument: whether someone is an introvert or an extrovert. And I'm not talking about the "introvert=shy" that has pervaded common culture, but the actual psychological definition of the two which is about how people use and recharge mental/emotional energy. Extroverts are energized by social interaction, regardless of whether they're shy or not, while introverts are exhausted by it. So introverts naturally have a more transactional relationship with social interaction because they have to. If they didn't, they'd emotionally and mentally burn out. So to an introvert, any social interaction has to be weighed against how much mental and emotional energy they're willing to invest into it, and cultural formalities with people you don't know or care about to simply fill periods of silence with human noise would therefore fall very far down the list of things that they want to do. Whereas an extrovert, for whom basically any conversation could be like water to a parched plant, would delight at pretty much any chance to engage any random person.

So what we really have in this thread is introverts saying that they'd rather spend their limited daily emotional labor on the people they love than random strangers and extroverts mystified by the concept that anybody would balk at the opportunity for stimulating conversation.