UEFI (Unified Extensible Firmware Interface) is a modern firmware interface that initializes computer hardware and starts the operating system when a system is powered on. It replaces the legacy BIOS and provides a more flexible, extensible, and secure framework for the boot process. UEFI supports features such as Secure Boot, faster startup times, graphical configuration interfaces, and the ability to boot from large storage devices using the GUID Partition Table (GPT).
UEFI operates between the system firmware and the operating system, performing hardware initialization and handing control to the OS bootloader. It also allows firmware-level drivers and applications to run before the operating system loads, enabling advanced configuration, diagnostics, and security capabilities.