In plain English
Sentiment analysis is a natural language processing technique that determines the emotional tone behind a piece of text, typically classifying it as positive, negative, or neutral. It lets organisations measure mood at scale across many messages. It is widely used to track customer feedback and social media reaction.
A worked example
A brand runs thousands of product reviews through sentiment analysis to see, at a glance, whether reaction to a new feature is mostly positive or negative.
Common confusion
Sentiment analysis can miss sarcasm, irony, and context, so a clearly negative review can be misread as positive when the language is playful.