The term "1977 trinity" has been used, here on Retrocomputing SE and elsewhere, to refer to a set of three computers that started shipping in mid- to late-1977: the Apple II, the TRS-80 Model I and the Commodore PET 2001.
This kind of term does not seem to have been unusual; the Japanese had an almost identical one (allowing for cultural differences) by the early '80s: 「御三家」 (gosanke), referring to their trinity of the Hitachi Basic Master, Sharp MZ-80K and NEC PC-8001. (With the rise of 16-bit machines this term was later amended to 「8ビット御三家」, hachi-bitto gosanke.)
Wikipedia mentions the "1977 trinity" in several places, but their reference is to the web version of a BYTE magazine article from almost twenty years later: "Most Important Companies" (BYTE Vol 20 No 9, Sept. 1995, p.99). It says, under "Commodore International" (p.100),
But along with Apple and Tandy, it was one of the 1977 Trinity: the three companies who brought out ready-to-run PCs.
But I can't find any references to the term in contemporary issues of BYTE. Carl Helmers' column "Reflections on Entry into Our Third Year" (BYTE Vol 2 No 9, Sept. 1977, p.6) says,
The "appliance" computer, a complete system presented in an assembled and tested package is on the threshold of its ultimate dominance in the general purpose personal computer field: from the high end, moving down in price, we find products like the Apple-II and the Commodore PET 2001 machines....
The last half of 1977 represents the entry of several relatively large concerns into the marketplace, in the form of Heathkit this summer and Commodore soon to follow. Rumors have it that companies ranging from Atari...to Radio Shack and Texas Instruments are in the process of developing general purpose systems appropriate for personal computing uses.
No other computer, much less "trinity," is mentioned in BYTE's coverage of the PET announcement, "Commodore's New PET Computer" (BYTE Vol 2 No 10, Oct. 1977, p.50), or the TRS-80 announcement, "The TRS-80: Radio Shack's New Entry" (BYTE Vol 2 No 11, Nov. 1977, p.446).
A quick scan of the tables of contents of BYTE from September to December of that year shows nothing else that looks like it would mention this "trinity," either.
So was this term really first coined in 1995, or were people using it earlier?