The tag description for EFI is :

EFI stands for Extensible Firmware Interface, and is an updated version of BIOS. It sits between firmware and the operating system in the software stack.

while UEFI is :

The Unified Extensible Firmware Interface BIOS (UEFI) is a specification that defines a software interface between an operating system and platform firmware. UEFI replaces the Basic Input/Output System (BIOS) firmware interface originally present in all IBM PC-compatible personal computers

Intel transferred development of the EFI specification to the Unified EFI Forum in 2005 who say in their FAQ

What is the relationship between EFI and UEFI?

The UEFI specification is based on the EFI 1.10 specification published by Intel®, with corrections and changes managed by the UEFI Forum. Intel still holds the copyright on the EFI 1.10 specification, but has contributed it to the Forum so that the Forum can evolve it. There will not be any future versions of the EFI specification, but customers who license it can still use it under the terms of their license from Intel. The license to the Unified EFI Specification will come from the Forum, not from Intel.

Currently there are 1380 questions tagged with UEFI and 388 with EFI.

There are a very few questions relating to old Macs (like this Update MAC EFI to EFI 2.x) where the EFI tag does actually mean EFI 1.10 but the vast majority of the EFI tagged questions in fact refer to UEFI.

Would it make sense to merge EFI into UEFI, or, as stackoverflow have done, make them synonyms?