Definition
Sentiment is how favourably an answer describes a brand when it names it: recommended without reservation, mentioned with a caveat, or named as the option to avoid. It is separate from whether the brand was named at all.
Why it matters
A rising mention rate with negative sentiment is a worsening situation that a visibility dashboard will report as progress.
How to measure it
Judge it from the full answer rather than a short excerpt, and leave it null when the answer is neutral or the judgement is uncertain instead of forcing a label.