ROM is an acronym of Read Only Memory. ROMs are computer memory chips with permanent read-only data. ROMs are used for storing an operating system (KERNAL), a BIOS, an OS or a character set. The C64 is supplied with BASIC in a bootable ROM.
A variation of the ROM is the EPROM (Eraseable Programmable Read Only Memory). EPROMs are rewriteable via EPROM burners, such as Tiny Eprommer. Errors can occur during reprogramming, leaving the dependent device or peripheral ‘bricked,’ meaning it won’t work correctly!