BIOS in part refers to the firmware code run by a PC when first powered on, which is a type of boot loader. The primary function of the BIOS is to identify and initialize system component hardware (such as the video display card, hard disk, and floppy). This is to prepare the machine into a known low capability state, so other software programs stored on various media can load, execute, and assume control of the PC.[3] This process is known as booting, or booting up, which is short for bootstrapping. Among other classes of computers, the generic terms boot monitor, boot loader or boot ROM were commonly used. Some Sun and Macintosh PowerPC computers used Open Firmware for this purpose. There are a few alternatives for Legacy BIOS in the x86 world: Extensible Firmware Interface, Open Firmware (used on the OLPC XO-1) and coreboot.

Source: Wikipedia (http://en.wikipedia.org/wiki/BIOS)