Short for Unified Extensible Firmware Interface, UEFI is a specification that defines a more modernized model for the interface between computer operating systems and platform firmware during the boot, or start-up, process.
UEFI originated as the Intel Boot Initiative in the late 1990s before being turned over to the Unified EFI Forum, and today the forum and specification remain the result of a collaborative effort between computer processor manufacturers like AMD and Intel and software operating system companies like Microsoft and Apple.
In many ways, UEFI serves as a software-driven, bare-bones operating system that can sit on top of the legacy BIOS boot process, and like BIOS, UEFI is responsible for initializing the hardware of a device or computer before passing control of the hardware to the operating system. Most newer computer platforms support both UEFI and legacy BIOS booting in order to ease the transition to UEFI and accommodate older operating systems that don't have built-in UEFI support.
The UEFI specification offers advanced features over BIOS such as secure boot, low-level cryptography, network authentication and universal graphics drivers. The Secure Boot functionality in UEFI provides the basis for the Microsoft Secure Boot feature in Windows 8 that enables the OS to detect rootkits and similar malware attacks.