When I started out, I had music stored on my NAS along with a "Server" program designed for the Linux OS on the NAS. I called the NAS my "Server". It was controlled by a different company's software from an app via the Upnp protocol.
Jim,
"Server" is a generic name used by a whole class of gizmos. Its is like the term "automobile". An automobile can be passenger car, pickup truc, tractor or an 18-wheeleter.
In your specific case, NAS (Network Attached Storage) is a server for sure, but to be specific, it is a file server. So "File Server" or "NAS server" are really good terms to use. If you are using Roon, the computer on which roon is running is the "Music Server'. All this music server does it take the music files from the NAS and push it over the network the music player. Typically, music player is on a separate/dedicated server.
The term renderer is a little tricky. I have two setups running now.
An AP-Linux server. On this server, only linux music player MPD is running. Music directories from the NAS are mounted. IOW, the music files look as if they are locally available to MPD. MPD itself maintains music library and responds to commands locally or via an app on android or IOS. In this setup, as there is "Network Streaming" involved, there is no renderer.
Once the network streaming is involved, there is a protocol for transferring and playing media files, DLNA (Digital Living Network Alliance). Your roon system and my Audirvana fall in this category.
A renderer does not do any media management, it only plays the media file it receives over the network. In your case, roon player is the renders and in my case MPD player is the renderer. (disclaimer: Strictly speaking MPD is not a renderer as it is DLNA compatible software. Another piece of software residing on the music player, uPnpMPD, receives the media data over the network and fees to MPD player locally).
I think, in Roon world, Music management and music server part of the system also does the (up/re)sampling of the music data. Roon player (renderer) is not involved. In my Audirvana system, resampling is done by a different piece of software (libsamplerate) which is residing on the music player computer handles the resampling operations. So, resampling becomes part of the renderer in my case.