A sentence is a group of words that expresses a complete thought. Sentence sections, also known as phrases, are the individual parts of a sentence that each have their own meaning. Phrases can be made up of one or more words and can be used to modify other words in the sentence. They are usually separated from the rest of the sentence by commas or other punctuation marks. Examples of phrases include noun phrases, verb phrases, adverb phrases, and prepositional phrases.