The phrase "ad hom" is a shorter version of "ad hominem," which means attacking or criticizing someone's character or personal qualities instead of addressing their argument or viewpoint. Full definition
Anyway, the whole argument is just a smear against those who work on models like NASA GISS Model E. It's a form of ad hom dressed up in the cloak of authority. (realclimate.org)
Ad homs aside, my point was that you can't average measurements that were never measured. (judithcurry.com)