System file used by both Intel-based computer systems and computer devices such as AppleTVs; contains system-level data that executes between the operating system and the firmware; used for staging firmware updates, booting operating systems, and running pre-boot programs.
Using EFI files, systems can hand off the pre-boot process to a controlled environment. For example, EFI files are sometimes included with firmware updates and are loaded into the device's EFI System partition during the boot process. Here, the executable content in the EFI file safely runs the procedures necessary to update the device.
NOTE: The EFI specification, originally developed by Intel, was updated to the UEFI specification, which stands for "Unified Extensible Firmware Interface." The UEFI standard is maintained by the UEFI Forum.