Sentiment analysis (also known as opinion mining) is a natural language processing technique used to identify and extract subjective information from text. This technique is commonly used to analyse opinions, attitudes and emotions in social networks, blogs, reviews and other forms of online communication.

Sentiment analysis involves the use of algorithms and natural language processing tools to analyse text and determine whether the opinions expressed are positive, negative or neutral. It can also identify the emotional tone, the level of intensity of the emotions expressed and the keywords that indicate the author's opinion.

Sentiment analysis is used in a variety of applications, such as market research, online reputation management, customer service and business decision making. For example, a company might use sentiment analysis to assess customer opinion about a new product or service, or to identify and respond to customer issues on social media.

Sentiment analysis is also used in politics and public opinion, where it is used to assess public opinion on issues and political leaders. Overall, sentiment analysis is an important technique for understanding customer opinion, public opinion and for informing business and political decision-making.