ROM on android phones isn't really "read only"... right?

I see the word ROM and internal memory used interchangeably in the context of Android phones. The OS seems to be stored in the internal memory itself, which is also used for installing applications. Which implies that it is not "read only".

So, just to clear my confusion, am I correct in understanding that in Android phones the OS is stored in the internal memory and word "ROM" is used for "historic" reasons, since ROM is where firmwares on non-Android phone were/are otherwise commonly installed?