The phrase a/the member of a/the family unit is used in various pieces of Australian legislation, defined in various ways for various purposes. One legal office abbreviated it (in writing) as MOFU. Unfortunately, I can’t see that without thinking of something else less legal (indeed illegal) involving a member of a family unit.

Google’s first results are sales and marketing websites explaining TOFU, MOFU and BOFU, which apparently are the top of the funnel, the middle of the funnel and the bottom of the funnel respectively, which a) isn’t what I was thinking of, and b) makes me none the wiser.