The non-volatile storage location of system BIOS, typically in electronically erasable programmable read-only memory (EEPROM) flash memory on the motherboard. While system flash memory is a technology-specific term, guidelines in this document referring to the system flash memory are intended to apply to any non-volatile storage medium containing the system BIOS.
Source(s):
NIST SP 800-147
NIST SP 800-147B