What is "a word belonging to the part of speech that expresses an action?

The part of speech that expresses an action is called a verb. A verb is a word that describes an action, occurrence or state of being. Some common examples of verbs include run, walk, jump, sing, dance, eat, and sleep. Verbs can be used in a variety of tenses and moods to indicate the time and manner of an action or event. They can also be used in various forms, such as infinitives, participles, and gerunds. In many cases, the verb in a sentence serves as the main predicate, indicating the action or state of being of the subject. Verbs are an essential part of any sentence or phrase, as they help to convey meaning and provide context.