In linguistics, the topic (or theme) of a sentence is often defined as what is being talked about, and the comment (rheme or focus) is what is being said about the topic.This division of the information structure of the sentence is generally agreed upon, but further than this the definition of what constitutes a "topic" is controversial and depends on which particular grammatical theory is being employed.

The difference between "topic" and grammatical subject is that topic is used to describe the information structure, or pragmatic structure of a sentence and how it coheres with other sentences, whereas the subject is a purely grammatical category. For example it is possible to have sentences where the subject is not the topic, for example often the case in passive sentences. In some languages word order and other syntactic phenomena is determined largely by the topic-comment structure, rather than by the grammatical structure of the sentence, these languages are sometimes referred to as topic-prominent languages, Chinese is often given as an example of this.

Topic or Topicality may refer to:

A comment is generally a verbal or written remark often related to an added piece of information, or an observation or statement. These are usually marked with an abbreviation, such as "obs." or "N.B.". The term "comment" may have different meanings depending on specific fields of usage.