AO - area of operation.
Back flag - the flag closest to your spawn.
Front flag - the flag farthest from your spawn.
Middle flag - flag in the middle of a 3 or 5 flag map.
FECN - fully equipped combat nurse.
FECM - fully equiped combat medic.
blueberries/smurfs - any one who isn't in your squad (usually relating to randoms).
Unit - a single person/ vehicle (often used in call outs).
SMK - short for smoke.
VOIP - Voice over IP (set to team or squad in game).
CMM - counter mortar measures / mission.
Flank - a route pertaining to a side of a map used to get on the side, or behind an enemy group (THERE IS NO MIDDLE FLANK).
Wookie - a recon who has set up shop far away from action, often found near/in vegetation.
Base - the place in which enemy units spawn and have most armor to start off.
Route - any path, whether secluded or open, that involves moment for an objective.
Any others you guys want to add , just post here and iLL delete the post and merge it with this one :]