CMOS stands for Complimentary Metal-Oxide Semiconductor. It is a chip that stores the system time and settings. It is saved by a battery.
BIOS stands for Basic Input Output System. It's responsibility is to handle all the basic operations of the computer from power up, such as initializing circuits, telling the computer how to utilize the drives, loading the operating system, handling the I/O between devices such as the keyboard and mouse, etc.. It is programmed into a ROM.