Intransitive verbs are action verbs that do not require a direct object to complete their meaning. This means that the action does not pass onto someone or something else. For example, in the sentence "The dog barks," the verb "barks" is intransitive because there is no object receiving the action. Intransitive verbs can often be followed by adverbs or prepositional phrases that provide additional information. For instance, in "She runs quickly," the adverb "quickly" describes how she runs, but there is still no direct object involved. Understanding intransitive verbs helps clarify sentence structure and meaning in language.