are substitutes for nouns, e.g., Judy sat at her computer and turned it on.

A pronoun is one example of a part of speech. Pronouns are typically small common words used to reference things already indicated in the conversation. For instance, in the sentence "I didn't find the book, because I had lost it the day earlier", the word it is a pronoun used to reference the object of the previous clause, namely the book.[ edit

are often used to refer to a noun that has already been mentioned. 'She', 'it' and 'who' are all examples of pronouns. Cambridge Online Dictionary