A pronoun is a word that refers to a noun to avoid repetition. The main types of pronouns are possessive, demonstrative, interrogative, reciprocal, relative, intensive, reflexive, personal, and indefinite pronouns. Examples are provided for each type, such as "my" and "your" for possessive pronouns, "this" and "that" for demonstrative pronouns, and "who", "whom", and "what" for interrogative pronouns.