Stations and equipment manufacturers have been incorrectly calling HD Radio High Def and High Definition Radio. I have always identified HD Radio with its ficticious inventor, Hoss Dorfmeister. I just found a third interpretation at IBM.com, which equally has no basis in fact:
"...In the case of Radio, HD stands for Hybrid Digital, according to iBiquity.
And that settles it"
"...In the case of Radio, HD stands for Hybrid Digital, according to iBiquity.
And that settles it"