Read-Only Memory (ROM) is a type of computer memory that permanently stores data and basic instructions that don't change, such as the firmware that starts up a computer (BIOS/UEFI). Unlike RAM, which loses data when power is off, ROM retains its contents permanently. ROM is 'read-only' because its contents are set during manufacturing or can only be changed through special processes, not during normal computer operation. While traditional ROM was truly unchangeable, modern variants like EEPROM and flash memory allow updates. ROM ensures computers have the basic instructions needed to boot up and access other components before loading operating systems from storage.