next time start with the truth.
HEADSPACE is a characteristic of a chamber and bolt face. typically not adjustable, see gunsmith and savage rifles.
HEAD CLEARANCE.. is making sure the case is small enough so it fits and the bolt can close.
this is an adjustment that can be made by adjusting your sizing die.
I don't think being pedantic is in the best interest of a newbie. Technically you're correct, however not even Hornaday uses that term. The tool I referenced was the Hornaday HEADSPACE COMPARATOR (my emphasis), not headspace clearance comparator. So the term I used was correct as most hobbyist and the industry understand it. I'm sensing the imminent return of a certain member who liked to rail about headspace having nothing to do with cartridge sizing. You're not him, though.
Further reinforcing that, I made a search here for your preferred term, and found ONE return from 2008. How is that going to help a newcomer?
I also used the term "basically" and described H.S as fit to the chamber which is absolutely correct. When installing a barrel, I use a H.S. gage to set the barrels relationship to the bolt head so that the correct amount of unsupported cartridge is protruding from breech face per SAAMI specs. That's a one time adjustment that is made to insure that cartridges also made per SAAMI specs will fit properly, and not FTF due to excessive headspace. And there's where the commonality in terms comes in. If the cartridge fails to fire, is the headspace set too long, or is the cartridge's shoulder set too short, belted designs notwithstanding? (knew where you were going next)
And that's where the value of a headspace discussion is relevant to setting up a FL sizing die.
So beside being pedantic and irritating, even insulting, what are you adding to the conversation that is helpful to the new guy?
By the responses I'm reading it appears to myself and others that the answer to that is NOTHING.