firmware

The permanent software programmed into a hardware device's read-only memory to manage low-level data operations.

Firmware acts as the critical translation layer between hardware circuitry and high-level software. It resides in non-volatile storage like ROM, EPROM, or flash memory, ensuring the device remains functional even after power loss. From the BIOS/UEFI that initializes a PC motherboard to the RTOS controlling a Bosch fuel injector, firmware executes the essential instructions that define a machine's identity. Modern implementations (such as those found in Apple’s M-series chips or Tesla’s motor controllers) allow for field updates, enabling hardware to gain new capabilities or security patches without physical intervention.

https://www.uefi.org