topic

Topic is the subject matter discussed, studied, or written about. It identifies the central idea around which a text or discourse is organized and helps readers understand its scope. Topics can be broad, such as history or biology, or narrow, such as the effects of a policy on urban traffic. Identifying the topic is a common first step in analysis and communication.

In linguistics and discourse analysis, the topic is the element of a sentence or discourse that signals what is being talked about, often before the comment. A sentence can focus on different topics depending on context and emphasis. The topic is not always the grammatical subject, but it often influences word order and perspective.

In information science, topic modeling aims to discover latent topics in a collection of documents. A topic is typically a probability distribution over words, and each document is a mixture of topics. Methods such as Latent Dirichlet Allocation (LDA) and non-negative matrix factorization are commonly used to infer topics from data.

Etymology: Topic derives from Greek topikos, via Latin topica, meaning “of place” or “local.” In modern use, topic is closely related to subject and theme, though topic tends to refer to the subject matter being discussed rather than the broader message.