"Sentiment" is the process of determining whether a piece of writing is positive, negative or neutral. It’s also known as opinion mining, deriving the opinion or attitude of a speaker. A common use case for this technology is to discover how people feel about a particular topic.
Say you want to know if people on Twitter think that Chinese food in San Francisco is good or bad.
"Sentiments" will answer this question. You immediately have a better idea of why the your talking partners aren’t happy.