DMG is different from dmg. DMG = Dungeon Master's Guide and dmg = damage and is used as a frequent written abbreviation, but I've never heard it pronounced except as a whole word.
words I'd add though some are probably out of use:
Monty Hall - game with lots of treasure and power building for the players with little corresponding challenge. (after Monty Hall, the host for Let's Make a Deal game show)
Campaign - a series of connected adventures featuring the same set of characters
Min/Max - carefully balancing a character, usually used in a derogatory sense for someone who worries more about numbers than character,
splatbook - source book
template - for quick but customizable character design, primarily used in point-based systems
for that matter, distinguish between "point-based" and "class-based" game systems.
Open Gaming Lisence (distinct from d20, but based on the d20 ruleset)
Mechanics - the rules of the game
balance - relative power and playability of various power sets or classes versus each other
contest/opposed roll - where two PCs, or a PC and an NPC roll to see who gets the better result
difficulty number - target for a die roll
encounter - any meeting between a PC and an NPC or monster
turn/round/segment - mechanics for time measurement
random tables - for determining randomly encounters, treasure, results, etc.
I'm sure I'll think of more. Read around on places like RPGnet and CM, they'll have some terms show up frequently.
I'd also submit that some terms on your list, like Dungeon Master and Epic level are primarily D&D terms and not generic ones, but you may still want to include them.
