The document discusses phrases and clauses. It defines a phrase as a group of words that makes some sense but not complete sense because it lacks a subject and predicate. Common types of phrases include noun phrases and adverb phrases. The document defines a clause as a group of words that forms a complete sentence with both a subject and predicate. Clauses can be main clauses or subordinate clauses like noun clauses or adverb clauses. The key difference between a phrase and clause is that a clause contains both a subject and predicate while a phrase lacks one or both.