The document discusses prefixes and how they are used to change the meaning of root words. It provides examples of common prefixes like "un", "mis", "pre", and "dis" and their meanings. It also explains that prefixes are added to the beginning of root words, and that this can change the spelling or create new words with different definitions than the root word alone. The document aims to describe how prefixes work and provide examples to illustrate their use in modifying root words.