Defining the Interface Between the Operating System and Platform Firmware
The Unified EFI (UEFI) Specification (previously known as the EFI Specification) defines an interface between an operating system and platform firmware.
The interface consists of data tables that contain platform-related information, boot service calls, and runtime service calls that are available to the operating system and its loader. These provide a standard environment for booting an operating system and running pre-boot applications.
The UEFI Specification was primarily intended for the next generation of IA architecture–based computers, and is an outgrowth of the "Intel® Boot Initiative" (IBI) program that began in 1998.
Intel's original version of this specification was publicly named EFI, ending with the EFI 1.10 version.
In 2005, The Unified EFI Forum was formed as an industry-wide organization to promote adoption and continue the development of the EFI Specification. Using the EFI 1.10 Specification as the starting point, this industry group released the following specifications, renamed Unified EFI.
The current version of the UEFI Specification can be found at the UEFI web site.
Intel® Platform Innovation Framework for EFI and UEFI specifications