Ok lets have a go at this

SO, by definition a "range merge" is an exploitative play when you take hands from one range and use them in another, for example you have Q9 on AJ985 now this is typically a hand you would not value bet, but you decide for expoitative reasons you WILL value bet on this occasion - you have in essence "MERGED" your check back and your value betting range together. This would be also known as a "thin value bet" lol.
In the same example, spose you have KJ, a hand you would usually value-bet, HOWEVER you decide for some reason to BLUFF with it on this occasion, you have merged your Value-betting range and your bluffing range together - this would also be known as "turning your hand into a bluff" (lol)
It's a pretty old concept, traditionally you'd turn the
worst hands you'd wanna check back into bluffs (because these have the least chance of winning at a showdown), you'd pick the
best hands you'd wanna check back into value bets (as these have the best chance of being called by worse) things have moved on a bit since then but i believe the basic theory that lies behind "merging your ranges" starts somewhere with that.
So a "triple range merge", imo would either be a hand that has gone through ALL the ranges - i.e you pick a hand from your value-betting range to bluff with (it's gone from value-bet, to pot control-to bluff) or visa versa you take a hand from your bluffing range and value-bet with it.
OR
It's a hand that you could either call, raise or fold (for value or as a bluff, or a combination of the two) with the idea to either bluff or valuebet a later street, in essence you don't have a value-betting, a checking or a bluffing range, you're using the same hand for all three (just depends exactly what you chose to do on this occasion)
Conclusion: I have no idea what a triple range merge is. The words don't even seem real.