A speech act is an utterance that serves a function in communication. It is a verbal action that accomplishes something, such as greeting, insulting, complimenting, pleading, supplying information, and getting work done. Speech acts can be a single word or a sentence, and they include real-life interactions that require not only knowledge of the language but also appropriate use of that language within a given culture.

Speech acts are difficult to perform in a second language because learners may not know the idiomatic expressions or cultural norms in the second language or they may transfer their first language rules and conventions into the second language, assuming that such rules are universal.

According to the theory of speech acts, the minimal communication unit is the realization of a certain kind of acts such as stating, questioning, ordering, describing, apologizing, appreciating, congratulating, etc. Every act is directly related to the intention of the speaker. The speech act consists of three levels: locutionary act, illocutionary act, and perlocutionary act.

The locutionary act is the performance of an utterance, which has a meaning in the traditional sense. The illocutionary act is what the speaker is doing in saying something, such as requesting or promising, and how one is trying to affect ones audience. The perlocutionary act is the effect that the utterance has on the listener.

In summary, a speech act is a verbal action that serves a function in communication, and it can be a single word or a sentence. It requires knowledge of the language and appropriate use of that language within a given culture. The theory of speech acts identifies three levels of speech acts: locutionary, illocutionary, and perlocutionary.