I actually wrote up a blog last month entitled Community Commentary: The Diablo III [Urban] Dictionary that you might find useful. It links to The Diablo III [Urban] Dictionary forum thread over on DiabloFans. Jaetch's comprehensive thread covers a wide range of popular terms and lingo used by Diablo III players in-game, on the forums, and elsewhere online.

Here's his entry for EHP:

"EHP: short for "effective hit points" or "effective health pool." This usually is tied hand-in-hand with topics regarding a character's overall defensive capabilities."