The document defines several parts of speech - adverb, gerund, infinitive, noun, adjective, and verb. It then discusses the concept of parallel structure, which means using the same grammatical form for elements that have the same function. Parallel structure involves using words, phrases, or clauses that are similar in length and form. The document provides examples to illustrate parallel and non-parallel structures using different parts of speech. It also discusses using parallel structure with clauses.