The BIOS, or Basic Input/Output System, is a firmware embedded on a computer's motherboard. It initializes hardware components during the booting process and provides a set of low-level routines for the operating system to interact with the hardware. The BIOS is essential for starting up the computer and loading the operating system, such as Windows or Linux. BIOS settings can be accessed during startup, allowing users to configure hardware settings, boot order, and system time. Modern computers often use UEFI (Unified Extensible Firmware Interface) as a more advanced replacement for traditional BIOS, offering additional features and improved performance.