Use the word nobody to mean "no one," or for someone who's completely unimportant or insignificant. It's not nice to call someone a nobody; everyone wants to be a somebody.
If nobody is at home, you can ring the doorbell for an hour and get no response, and if nobody in your family likes pizza, there's no reason to order it for dinner. Since nobody means "no person," it's come to also have the meaning "insignificant person." It's hard not to feel like a nobody when your sister becomes famous after starring in a popular movie.