A pronoun is a word that takes the place of another word. The most familiar type of pronouns are the personal pronouns such as she, it, you, they, and so on. Pronouns can serve a variety of other functions, such as the relative pronouns like that, which, and who, which introduce descriptive relative clauses. The demonstrative pronouns like that and this can also be used to modify a noun (“this idea”, “these results”); when used in this way, these demonstrative pronouns become demonstrative adjectives.