Final answer:
In conversation, turns are made up of turn constructional units which can be a single word, a phrase, or a clause. A phrase lacks a complete subject or verb, while a clause includes both and can be independent or dependent.
Step-by-step explanation:
Turns in conversation are composed of what are known as turn constructional units (TCUs). These units can be various lengths and complexities, including a single word (lexical TCU), a phrase or clause (phrasal/clausal TCU), and a sentence (sentential TCU). A phrase is a group of words that act as a single unit within a sentence but lacks either a subject or a verb. On the other hand, a clause is a group of words that includes a subject and a verb, which can be independent (can stand alone as a full sentence) or dependent (cannot stand alone).