- last post: 01.01.0001 12:00 AM PDT
X -- Xbox, the platform in which the game is played on.
Y -- "You're On" -- the phrase the Chief would've said to those sword-wielding Elites had that event in the trailer actually happen.
Z -- Zealot -- a rank of Elites.
EDIT: s'right, fools.
[Edited on 12/31/2006]