N3rdTek The contents stored on /system contain all software needed to run Android on that specific device including: drivers, configurations, scripts, applications, frameworks etc.
They are read-only for the user and only writable after remounting as a system user or superuser/root.
Therefore ROM can be considered a valid and correct term for the Android system's /system partition/ROM partition.
Then macOS is a ROM, Windows 11 is a ROM, Debian is a ROM, Arch Linux is a ROM, Raspberry PI OS is a ROM? Last week I upgraded my Ubuntu ROM?
What about operating systems that run on phones, and can execute some Android binaries, but are not actually Android variants, such as Sailfish OS? Should that be called a "ROM" because it can execute some Android binaries, or because it runs on phones, or for some other reason?
N3rdTek In other words, both OS & ROM are technically correct and this repeated meme needs to die.
I doubt that either the "ROM community" or the GrapheneOS community will crush the other in a linguistic sense.
Somehow the Android modder community decided to call their OS images "ROMs". Ok, but both before and after they started doing that lots and lots and lots of people weren't doing that and still don't do that. I don't think humanity would move forward if everybody agreed to replace all uses of "OS" and "system image" and "system partition" with ROM.
Probably the Android modder community will keep on referring to operating systems, and system images for those operating systems, as ROMs. And probably the GrapheneOS developers will keep objecting to GrapheneOS and GrapheneOS system images being referred to with that term. Whether or not it is "technically correct" to refer to macOS as a ROM, Mac users don't generally do that. Likewise, whether or not it is "technically correct" to refer to GrapheneOS as a ROM, GrapheneOS users don't generally do that. And, as background, the practice of the Android modder community is not the standard or normative practice when most users of most operating systems refer to those operating systems.