EFI stands for Extensible Firmware Interface (EFI)
It was originally developed by Intel as part of an effort to modernize the boot process for modern computers and portable computers. It specifically would pick up where the basic input/output system (BIOS) left off for all IBM PC clones.
The development of EFI stemmed from the Intel Boot Initiative, which addressed concerns about the limitations of using BIOS with large server platforms. BIOS is limited to a 16-bit processor mode due to it originally being designed for the Intel 8088 microprocessor. It also was limited to 1MB addressable space.
Unlike BIOS, EFI is processor-independent (not limited to x86 microarchitecture.) It also supports CPU-independent drivers via EFI Byte Code (EBC) and also provides administrators with a superior pre-OS environment, where networking and other features would be immediately available without further steps.
In 2005, the development of EFI was transferred to the Unified EFI Group, although Intel still owns and exclusively licenses the EFI 1.10 specification. EFI continues on as the Unified Extensible Firmware Interface.