ROM is a shortcut for Read Only Memory. This synonym stand for all computer-chips, which are inputed constant-datas, and the computer can only read these. For example a operating system (KERNAL), a BIOS, an OS oder a character set.
A diversification of the ROM-datas isn't normal possible.
The advancement of the ROM is the EPROM (Eraseable Programmable Read Only Memory). This kind of chip, can be reprogramming or deleting with an electric supplementary signal to update the BIOS or the firmware. Occur an error by updating, so must be the EPROM reprogramming again, also the device or the periphal don't work correct !