With many thanks to
More Champagne Sir? for
collating these originally and submitting them to this thread.
241 or 2for1 - Voucher received from BA when set level of expenditure on BA American Express card is reached. This gives a free ticket when purchasing one full miles redemption ticket.
AVOD Audio Video On Demand - An updated IFE system allowing users to watch TV programs/movies etc when they want with the option to pause, rewind, stop etc as needed.
B/H - Bulkhead Seat (At the front of each cabin, often providing extra legroom. However, BEWARE bulkhead often = bassinet = babies screaming
)
BA - British Airways
BA AmEx PP - British Airways American Express Premium Plus Card (or without PP to represent BA AmEx standard card)
BACON - BA Connect - BA regional domestic service
BAEC or EC - British Airways Executive Club
BMED - British Mediterranean Airways (franchisee of BA operating flights to Africa, Middle East & Central Asia. Tickets booked through ba.com)
CC - In context of Tesco, refers to Clubcard
CCR - Concorde Room - for pax ticketed in First class ex-LHR T4 only (or the lucky ‘101 Dalmations’ who hold a special Concorde Room pass, first issued on 2003 after the retirement of Concorde)
CE - Club Europe (European Business Class)
CPN - Coupon - Refers to Paper Tickets (becoming more and more unusual)
CSD - Cabin Services Director (Most senior member of cabin crew)
CSDM - Customer Service Duty Manager (Most senior member of airport ground staff)
CW - Club World (L/H Business Class)
DO - officially a gathering of 12 or more at an event intended for FlyerTalkers. In reality, a gathering of any number of people involving large amounts of Alcohol.
Click here for a list of all upcoming Dos.
Dusking -
not an acronym/abbreviation, but often seen on the board - refers to the process of a plane going from OCW to NCW, and also adding WT+ to L/H aircraft.
DYKWIA - Do You Know Who I Am? - Often heard by Gold BAEC members after being refused an upgrade. (Also Rick's handle!)
ECCA - Executive Club Corporate Agreement – a legacy scheme which BA ran for major corporate clients, with reduced thresholds for qualifying for Gold, Silver, etc. and various other benefits. Removed from use in July 2003, but still referred to on FT occasionally.
EF -
www.expertflyer.com - useful website which shows flight & seating availability for all carriers (incl. BA). Subscription is £2.95 per month, which can be cancelled at any time.
ex-EUR - refers to starting a journey from an out-station in Europe which often results in a significant discount in fare.
Click here for more info
Fare Classes - Not an acronym, but
click here for details
FBD - Fast Bag Drop (to be used at the airport after using SSCI or OLCI)
FFP - Frequent Flyer Program (e.g. BAEC)
FSB - Friends & Supporters of BA (new way of scoring BAEC members - only listed on the CSD's manifest) - this one's a fun fake, that I completely fell for!! 
GB - GB Airways (franchisee of BA operating flights to destinations around the Med. Tickets booked through ba.com)
GEx - Gatwick Express (Fast train between LGW and London Victoria)
GUF2 - Gold Upgrade for 2 voucher - voucher given to Gold members upon reaching 2500 TPs and again at 3500 TPs.
HA - Household Account
HEx - Heathrow Express (Fast train between LHR and London Paddington)
H.I. - Him/Her Indoors (Not a BA acronym but a very common FT one and deserves a place on this list)
IFE - In-flight entertainment
ISTR - I seem to recall/remember (not BA, but useful)
L/H - Longhaul
MCO - Miscellaneous Charge Order (a form of credit note given to passengers from BA
MFU - Miles for Upgrade (Method of redemption using cash + miles to upgrade)
MHC - Mile High Club (Ahem
)
MIC - BA missed interline connection
MMB - Manage My Booking (Tool for seeing details about your booking)
MVCC - Most Valued Corporate Client
NCW - New Club World (New style of Business Class - flat beds)
NGCW - Next Generation Club World (New style of Business Class replacing NCW)
NOCW - New Old Club World - Only found on BMED, this is a new style of BA's OCW Cradle seat.
NSFU - Not Suitable for Upgrade
OCW - Old Club World (Cradle style seats – now only found on BMED flights)
OLCI - Online Check-In
Op-Up - Operational Upgrade (free upgrade given for no specific reason)
OW or 1W -
oneworld (Aer Lingus, American Airlines, BA, Cathay Pacific, Finnair, Iberia, LAN, Qantas)
PCPM - Part Cash Part Miles (Another method of redemption using cash + miles. Generally considered a poor use of miles)
PFUG - Pre-Flight Upgrade
PNR - Passenger Name Record - also known as the BA Booking Reference
PUTI - Posting Under the Influence - VERY common on this board 
PYOBP - Print your own Boarding Pass
RDUG - Redemption Upgrade
RTW - Round the World ticket
S/H - Shorthaul
SAU - Space Available Upgrade
SEx or StEx - Stansted Express (Fast train between STN and London Liverpool St.)
SFU - Suitable for Upgrade
SM or SPML - Special Meal (e.g. Vegetarian, Kosher etc)
SS or S/S - Special Services (BA Staff as the airport usually in suits, to help VIP or Premier passengers with anything they need)
SSCI - Self Service Check-In
SSSS - Selected for Secondary Security Screening (printed on selected boarding passes usually ex-USA meaning you're going to be extra checked by security)
T1/T2/T3/T4 - LHR (London Heathrow) Terminal
TATL – TrAnsaTLantic (as in a ‘TATL trip’)
TCP - To Complete Party - Used where you have two separate bookings on the same flight (e.g. you and spouse) and want to join the bookings up to ensure you sit together.
TFTG - Tales from the Galley (kindly provided to us from
Pucci,
Purserette,
Tits (see below) and a few other BA Lurkers.
Click here for a great example)
Tits - Again not an acronym, but worth mentioning to avoid confusion... Tits is short for
Tits McGhee who is one of our BA Cabin Crew Lurkers.
TP - Tier Points
WT - World Traveller (Economy)
WT+ or WTP - World Traveller Plus (Premium Economy)
WW - Willie Walsh (aka "The Boss"), BA’s current CEO.
YUP - Type of American Airlines fare (pronounced Y-Up) that books into very cheap First class, but gets full allowance of BAEC F TPs
And finally....
FT -
FlyerTalk!!!
In addition, check out the official FT Glossary for general (non-BA specific) abbreviations,
click here.