Good question 

Wikipedia defines a firmwares as follows:

In electronic systems and computing, firmware is the combination of persistent memory and program code and data stored in it.[1] Typical examples of devices containing firmware are embedded systems (such as traffic lights, consumer appliances, and digital watches), computers, computer peripherals, mobile phones, and digital cameras. The firmware contained in these devices provides the control program for the device. Firmware is held in non-volatile memory devices such as ROM, EPROM, or flash memory [...]

On Internet forums (including the big ones such as xda-developers.com) both firmware and ROM terms are interchangeable. In my humble opinion this is a bit of an abuse of language as the firmware on our tablets and other Android devices aren't stored on ROM type memories but on flash memories or EPROM (for some specific hardware components). I don't know why this confusion is initially made, maybe it dates back to the ROM dump for games on the old console machines, but it's not exactly the same thing. Anyway this mixture looks to be quite persistent and nobody seem to really care... or I just didn't get it right 

Cheers.