This page: https://wiki.osdev.org/UEFI and few others which are rather creditable mention that UEFI is kind of an application which run on BIOS (legacy BIOS) and not a firmware If I got it right. Some others claim they just run together (BIOS + UEFI). This is not about calling UEFI "UEFI BIOS" mistakenly (its another thing, not my question).
But as far as I know BIOS and UEFI are firmware interfaces and alternatives to each other. BIOS is legacy and UEFI is more advanced modern alternative to it.
So what's the reality?