ESD: Electronic Support Desk
ETC: Electronic Travel Certificate
FA - Flight Attendant
FD - Fuel Dump
FFN: Frequent flyer number (in context, can also be Hyatt faster free nights.)
FT: Flyertalk.com
GA - Gate Agent
KSML: Kosher (special) Meal.
OW: One-way (in context, can also be Oneworld)
MR: Mileage Run (in context, can also be Marriott Rewards or Membership Rewards.)
O/D: Origin/Destination
OLCI: Online Checkin
PM: Pre-merger
RT: Round Trip
SDC: Same-day confirmed change
TATL: Transatlantic (e.g. JFK-LHR)
TCON: Transcontinental  (e.g. JFK-LAX)
TPAC: Transpacific  (e.g. JFK-NRT)
YQ: Fuel surcharges.


Classes of Service:
F: First
J or C: Business
Y: Coach

Alliances:
*A: Star Alliance
*S: Star Alliance Silver
*G: Star Alliance Gold
ST: Skyteam
OW: OneWorld (in context)

Airline codes:
A3: Aegean
AA: American
AC: Air Canada
AF: Air France
AS: Alaska
AV: Avianca
AZ: Alitalia
BA: British Airways
B6: JetBlue
CO: Continental
CX: Cathay Pacific
DL: Delta
ET: Ethiopian
EK: Emirates
EY: Etihad
FB: Flying Blue (joint venture of Air France and KLM)
HA: Hawaiian
JL: JAL
LA: LAN
LH: Lufthansa
LX: Swiss
LY: El Al
NH: ANA
QF: Qantas
QR: Qatar
RJ: Royal Jordanian
SQ: Singapore
TG: Thai
TK: Turkish
UA: United
US: USAirways
VS: Virgin Atlantic
VX: Virgin America
WN: Southwest (also abbreviated as SWA)
 


Hotels:
HGP: Hyatt Gold Passport
(GH=Grand Hyatt, HH=Hyatt House, HP=Hyatt Place, HR=Hyatt Regency, PH=Park Hyatt)
HH: Hilton
IC - InterContinental
MR: Marriott Rewards (in context)
PC: Priority Club
SPG: Starwood Preferred Guest


Credit card points:
MR: AMEX Membership Rewards (in context)
TY: Citi Thank You points
UR: Chase Ultimate Rewards