WTT
Want to Trade
XP
Experience Points, these are needed to level up
ZA
Zul'Aman, a Level 70 10-man raid instance in Ghostlands
Zerg
To attack something with a lot of players/units, often leaving very little in terms of defense.
ZF
Zul'Farrak, an instance in Tanaris
ZG
Zul'Gurub, a level 60 raid instance in Stranglethorn Vale