The document discusses infinitives and infinitive phrases. It defines an infinitive as a verb form that begins with "to" but behaves like a noun, adjective, or adverb. Infinitive phrases begin with an infinitive and include any modifiers. The document provides examples of infinitives functioning as nouns, adjectives, adverbs, and within infinitive phrases. It also discusses how to identify the role of infinitives using a specific order or steps.