A bookworm is someone who loves to read. If you're a true bookworm, you'd rather spend Friday nights on the couch with a book than out at a party.
Some people are bookworms from the moment they first learn to read, while others grow into their love of books and reading after encountering a particularly wonderful book. Even people who didn't love the "Harry Potter" series of books mostly concede that they created a whole generation of bookworms. The word bookworm originally referred to a variety of insects that infest and eat paper, including the pages of books.