How it works defines what a ROM is, all of your incorrect web definitions aside. Go to somebody who works with this stuff (like I did) and say "ROM" and he'll say "This needs to be masked at the foundry, do you need me to design a mask? Better make sure your program is 100% correct because there's no going back" Say "PROM" and he'll say "I have to burn it, how many do you want? I'll give you the first one for testing before you tell me to burn the rest. If you want too many, might as well have ROMs made instead." He won't say "Oh, it's a writable ROM" because the concept of a writable ROM is rediculous, and the entire procedure, planning and business process around one is completely different.
Dandy. But the acronym ROM defines usage, not how it works.