"Fabulous" isn't a real name, so it doesn't have a real name! It's often used as a nickname or a term of endearment, meaning something that is extremely impressive, stylish, or enjoyable.
Do you have another question in mind? Perhaps you were thinking of a specific person who uses "Fabulous" as a nickname, or maybe you're curious about the origin of the word itself? Let me know and I'll do my best to help!