More technically speaking, BIOS is a holdover from the original 16-bit IBM designed Basic Input Output System (Hence BIOS).
It was used until UEFI replaced it around 2012sh (don't quote me on that, may be earlier or later depending on board maker). UEFI is a complete ground up 64-bit rewrite of old 16-bit legacy bios code. Most (all really) UEFIs also include a 16-bit "CSM" module to implement compatibility functions for devices that don't have their own 64-bit UEFI rom code up to date or ready.
UEFI's main achievements are invisible to the end user. But the most visible one is whether you do a legacy or non-legacy "UEFI-style" install. The only real benefit (besides secure boot) doing a proper UEFI install yields you is the ability to use the GPT partition table, which is much more flexible and allows drives over 4TB (vs legacy MBR).