I was under the impression that it was simply the file format used by llama.cpp and ggml, name inspired by the name of the author (https://github.com/ggerganov): https://github.com/ggerganov/ggml/blob/master/docs/gguf.md

He prefixes everything with “gg” (his initials).

EDIT: Confirmed: https://github.com/ggerganov/ggml/issues/220

The UF stands for Unified Format.