Nonfinite verbs are verb forms that do not show tense, person, or number. They include infinitives (e.g., to run), gerunds (e.g., running), and participles (e.g., run in "the run dog"). Nonfinite verbs can function as nouns, adjectives, or adverbs in a sentence, allowing for more complex sentence structures. These verbs are essential in English grammar because they help convey actions or states without being tied to a specific subject or time. For example, in the sentence "I enjoy running," the gerund running acts as a noun, indicating the action enjoyed by the subject.