I'm going to go out on a limb here and guess that you don't work in a large team with other developers, maintaining a common codebase.
I am pretty sure this is the case. I have worked with small and large teams. Large teams usually have a lot more abstraction in terms of their architecture. So there is most likely a "backend" app that is just an API and you consume it in your "frontend" (node, rails, etc) whatever that may be.
Frontend in this context is just another server that is communicating with backend APIs using RPC. When small teams think of frontend, they usually think about a framework like React, etc and pair it with a backend like Rails.