A PC BIOS stored in a flash memory chip rather than a ROM chip. Years ago, the flash BIOS replaced the ROM BIOS to allow for updating in place. Updating a ROM BIOS meant removing the chip and replacing it with a newer version. See BIOS, firmware, firmware update and flash memory.
Under Windows 95/98, the virus additionally discards the CMOS memory settings (CMOS contains the computer boot up hardware settings) and, just like the "Chernobyl" (CIH) virus, destroys data in FLASH BIOS microchip.