Unified Extensible Firmware Interface

Overview

The Unified Extensible Firmware Interface (UEFI) is a specification that defines a software interface between an operating system and platform firmware. UEFI is primarily used to define firmware services used to boot an operating system on a platform, but does add a few runtime services. The specification is published by the UEFI forum, where Arm is a board member.
For more detail on the specification, see here.