!!! Overview 
[{$pagename}] ([UEFI]) is a [specification] by the Unified EFI Forum[2] that describes an interface between the [Operating System] ([OS]) and the platform [firmware].[1][{$pagename}] replaces the [Basic Input-Output System] ([BIOS]) [firmware] interface originally present in all IBM PC-compatible personal computers while providing legacy support for [BIOS] services. 
[{$pagename}] can support remote diagnostics and repair of computers, even with no [Operating System] installed.

[{$pagename}] is in the form of data tables that contain platform-related information, and boot and runtime service calls that are available to the OS loader and the OS. Together, these provide a standard environment for booting an [Operating System]. This specification is designed as a pure interface specification. As such, the specification defines the set of interfaces and structures that platform [firmware] must implement. Similarly, the specification defines the set of interfaces and structures that the OS may use in booting. How either the firmware developer chooses to implement the required elements or the OS developer chooses to make use of those interfaces and structures is an implementation decision left for the
developer. 

[{$pagename}] replaces the [Basic Input-Output System] ([BIOS]) [firmware] interface originally present in all IBM PC-compatible personal computers, with most [{$pagename}] firmware implementations providing legacy support for BIOS services. 

Where BIOS interfaces require the OS loader to have specific knowledge of the workings of certain hardware devices the [{$pagename}] specification provides [Operating System] loader developers with abstracted interfaces that make it possible to build code that works on a range of underlying hardware devices without having explicit knowledge of the specifics for each device in the range. 

[{$pagename}] can support remote diagnostics and repair of computers, even with no operating system installed

[{$pagename}] is an enhancement of the [Intel] developed the [Extensible Firmware Interface] ([EFI]) specification. Some of the [EFI]'s practices and [data] formats mirrored those from [Microsoft Windows]. In 2005, UEFI deprecated [EFI]. The Unified EFI Forum is the industry body that manages the UEFI specification.

[Das u-boot] and [coreboot] are projects to move [{$pagename}] to [Open Source]

!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [UEFI Specification Version 2.7|http://www.uefi.org/sites/default/files/resources/UEFI_Spec_2_7.pdf|target='_blank'] - based on information obtained 2017-11-21- 
* [#2] - [ABOUT UEFI FORUM|http://www.uefi.org/about|target='_blank'] - based on information obtained 2017-11-21- 
* [#3] - [Unified_Extensible_Firmware_Interface|Wikipedia:Unified_Extensible_Firmware_Interface|target='_blank'] - based on information obtained 2017-11-21-