HBD stands for Human BioDiversity. I think it was a movement named and started by Steve Sailer.
John Derbyshire writes about the following Donald Trump quote:
[I] went to a great school … excellent student … smart guy … My uncle was a professor at MIT. He was a smart guy, y’know?—good smart guy. Right? Good family! Do we believe in the gene thing? I mean … I do. Right? Y’know? I do. Like they used to say, Secretariat doesn’t produce slow horses … [At 13m00s in this clip of The Donald addressing a campaign rally in Mobile, Alabama, August 21st 2015.]
Good grief! A Presidential candidate who is not a blank-slatist? Strange times, strange times.