Pronouns are words that replace nouns in sentences, helping to avoid repetition. They are categorized into several types, including personal pronouns, which refer to specific people or things (e.g., I, you, he, she, it, we, they), and possessive pronouns, which indicate ownership (e.g., mine, yours, his, hers, ours, theirs). Another category is demonstrative pronouns, which point to specific items (e.g., this, that, these, those). Additionally, interrogative pronouns are used to ask questions (e.g., who, what, which), while relative pronouns connect clauses (e.g., who, whom, whose, which, that). Each category serves a unique purpose in communication.