I found that I am confusing between web framework and web server.
Apache is a web server.
Tornado is a web server written in Python.
I just used Node.js for the first time to create a Discord bot. My thought was "Wow, Node.js is a server? I thought it was a JS library!" Or perhaps I could have thought about it as a framework.
Is it a web server? No but you can make one with it. Is it a server? As in the software that receives queries and serves the result? Yes.
In my case, I have issued the command:
node index.js
And now Node.js is waiting for requests to respond to (via my bot). It's a server, but it isn't serving web pages.