I don't know what the letters stand for but this was definitely a Microsoft (and ASCII Corp.) project for standardization of home computer hardware. Like XBox, but multi-vendor.

This is correct and it's mostly in Eastern part of the world. I owned a Spectravideo 328 when I was a kid. One of many kind of MSX computers.

The 328 was the precursor to the MSX standard. The 728 was MSX.

The differences were so small you could load most MSX programs on the 328 if you used a small software loader.

I learned this about 25 years too late. :-D

That was an afterthought, so that japanese companies didn't think they were directly tied to Microsoft.