I’d agree with BG’s definitions. A true “custom” home is one that’s uniquely built from the ground-up. It is not a “modified” tract, which some builders try to classify as “custom”.
I desperately wish we could go back to the days when families could buy their own lots and build their own, custom homes, however funky they may be. I HATE the big developers who’ve sucked up all of our land inventory, only to parcel it out and sell crappy, boxy, stucco boxes on tiny lots — with HOAs and Mello-Roos to boot. Yuck!!!!