BIOS - Basic Input Output System
Its a firmware, which has instructions stored to perform hardware initialization during booting and to provide runtime services for operating system
UEFI - Unified Extensible Firmware Interface
UEFI is same as BIOS with below advantages are.
Its supports partition more than 2 TB
It is quicker to boot up
It has got an actual graphical interface with animation and mouse support compared to BIOS boring blue screen