That's interesting
What it really means
A very common polite response to an idea or story. It often suggests the speaker does not really agree, or is not very interested, but wants to avoid saying so directly. Sometimes it is genuine, so watch the tone and what comes next.
Context, tips & common mistakes
"That's interesting" is genuinely ambiguous, and the tell is never the words — it is what happens next. Real interest produces a follow-up question within seconds ('interesting — how did you get into that?'); polite non-interest produces 'interesting' followed by silence, 'anyway', or a topic change, and the kindest reading is 'I have nothing to add and would like to move on'. Delivered flatly in a meeting, it can shade all the way into disagreement.
Calibrate your own use the same way: if you say 'that's interesting' and mean it, prove it with a question, because Brits apply the same decoder to you. And when your idea receives a naked 'interesting' from a supervisor, treat it as an invitation to strengthen the case, not as applause.