I usually speak to fertility (things that progressed at all vs clears), and viable hatch rate vs total hatch rate.
So if 15 of 20 eggs are fertile/progress, that's a fertility rate of 75%, but 5 of those eggs quit or are DIS at hatch, that's a viable hatch rate of 67%. The total hatch rate would 50%.
Sometimes I even break it down further into the post-lockdown hatch rate, so I can see where things were just quitters versus where I had issues with hatching.
As a person who uses shipped eggs, I find this to be helpful, because it lets me figure out:
1) How many eggs I actually need to order based on my past experience;
2) Which sellers (or shipping routes) don't do well for me; and
3) Where the problems are with my technique/equipment.
All that to say . . . unless people are being specific, I don't think you can assume what a hatch rate means, but I concur with hysop that two numbers don't give you the whole picture.