The abbreviation "BIOS" stands for Basic Input/Output System, a firmware interface that initializes computer hardware during the booting process. BIOS performs essential tasks such as hardware checks and loading the operating system from storage devices. It serves as a bridge between the operating system and the hardware, ensuring that all components are functional before the system starts. BIOS settings can also be configured for hardware management and system settings, making it crucial for the overall functionality and performance of a computer.