Small talk is light, casual conversation about everyday things, made to be friendly rather than to share anything important.
Two people waiting for a bus might say, Cold morning, isn't it? That short, easy exchange is small talk.
Seeing it in a sentence
At a party you barely know anyone, you might hear, So, have you tried the snacks? They're really good. That is small talk: an easy remark about something right there in the room, meant to be pleasant rather than deep.
In a sentence, you could say They made small talk for half an hour while they waited. Picture two strangers filling the quiet with safe topics like the weather, without expecting the chat to go anywhere important.
Small talk is not the same as a real conversation about your life or plans. If a coworker asks How was your weekend? and you answer Good, thanks, pretty quiet, that is small talk even if a short follow-up question like Did you do anything fun? keeps the exchange going for a minute. Light, brief exchanges between people who are not close are still small talk. It becomes something different when someone stops and shows deeper interest, asking about your weekend because they genuinely want to know what is happening in your life. That has moved from polite filler to a genuine exchange.
It also differs from a serious discussion. Small talk stays on safe, everyday subjects precisely so nobody has to argue or reveal much. Saying Traffic was awful on the way in is small talk; debating road policy in a heated way would not be.