Is having a secret password security by obscurity? What about a private key? Security by obscurity is about the bad practice of thinking that obscuring your me

Is having a secret password security by obscurity? What about a private key? Security by obscurity is about the bad practice of thinking that obscuring your mechanisms and implementations of security increases your security. It's about people that think that by using their nephew's own super secret unpublished encryption they will be more secure than by using hardened standard encryption libraries.