So once in a while I see the need for a new term in type design (yeah, like "bouma") generally to make discussion easier/clearer. This time it actually came to me as a result of reading a passage in Dreyfus's "Type specimen facsimiles" - so actually maybe this term was in fact used by people before - but I'd never seen it before, and it's sorely needed.
Depth: the degree of extenderness of a typeface. So for example Mrs Eaves is somewhat deep, while ITC Cheltenham is very shallow. We often need to say things like "the x-height is too generous", but that's too clunky. So instead you could say "it's too shallow". You could even say things like "the depth is good, but too high", meaning that the x-height is fine but the ascenders are too long compared to the descenders.
What do you guys think? Unless somebody convinces me otherwise I think I'm going to start using the term right now, probably with a little wiki to refer to. I just hope it doesn't take as long as bouma to engrain - that took a lot of work, and I'm not font-young any more.