A pen name is like a made-up name that a writer uses instead of their real name when they write books or stories. It's kind of like a nickname, but it's not really for fun or games. Sometimes, writers use pen names to keep their real identity a secret, so that people don't know who they really are. Other times, they might use a pen name because they want to write about something that they might be embarrassed or ashamed to talk about under their real name. It's like putting on a mask or a costume to become somebody else, except with writing. People have been using pen names for a long, long time - even famous authors like Mark Twain, George Orwell, and J.K. Rowling have used pen names!