The following is a list of the abbreviations and acronyms used by Cast Members and folks on the internet. Some abbreviations have multiple meanings and some destinations have multiple abbreviations.
AA - The American Adventure
AA - Audio-Animatronics [The *robot* characters in the attractions.]
AABBQ - All-American Bar-B-Que
AC - Adventurers Club
AE - The ExtraTERRORestrial Alien Encounter
AK - Disney's Animal Kingdom
AKL - Animal Kingdom Lodge
AP - Annual Passport
AP - Artist Point
APer - Annual Passportholder
AS - Disney's All-Star Sports Resort
ASM - Disney's All-Star Music Resort
ASMV- Disney's All-Star Movies Resort
BatB - "Beauty and the Beast" - Live on Stage
BB - Blizzard Beach
BC - Beach Club Resort
BCV - Beach Club Villas
BTMRR - Big Thunder Mountain Railroad
BW - Body Wars
BW - Disney's BoardWalk Resort
BWV - Disney's BoardWalk Resort (Villas)
CB - Character Breakfast [Breakfasts where Disney Characters show up.]
CBJ - Country Bear Jamboree
CBR - Disney's Caribbean Beach Resort
CG - California Grill
CM - Cast Member [An employee of the Walt Disney Company]
Cont - Disney's Contemporary Resort
CoP - Walt Disney's Carousel of Progress
CP - Candlelight Processional
CP - Crystal Palace
CRO - Central Reservations Office [handling Dining and Resort reservations]
CS - Disney's Coronado Springs Resort
CSR - Disney's Coronado Springs Resort
CTX - Countdown to Extinction (now called Dinosaur - Animal Kingdom)
D/MGM - Disney-MGM Studios
DAKL - Disney's Animal Kingdom Lodge
DC - Disney Club
DCA - Disney's California Adventure
DCR - Davy Crockett Ranch
DD - Downtown Disney
DL - Disneyland
DLH - Disneyland Hotel
DLP - Disneyland Paris
DLP - Disneyland Pacific Hotel
DV - Disney Village Marketplace
DVC - Disney Vacation Club
DVM - Disney Village Marketplace
DW - Walt Disney World Resort
DWWS - Disney's Wide World of Sports
DxL - Disney's Dixie Landings Resort, now Port Orleans Riverside
EC - Epcot
ECV - Electronic Convenience Vehicle (electric wheelchair/scooter)
EE - Surprise Mornings (early entry)
ELP - Main Street Electrical Parade (electrical parade)
FF - Flying Fish
FoTLK - Festival of the Lion King (Animal Kingdom)
FNF - Food and Fun
FtW - Fort Wilderness
FW - Disney's Fort Wilderness Campground
FW - Future World (part of Epcot)
FWH - Disney's Fort Wilderness Homes
GF - Disney's Grand Floridian Resort and Spa
GMR - The Great Movie Ride
GN - Grad Night
GoH - Guest of Honor [written as GoH '76 meaning the first year you visited WDW]
GSM - Guest Satisfaction Measurement
HISTA - Honey, I Shrunk the Audience
HM - The Haunted Mansion
HM - Hidden Mickey
HNY - Hotel New York
HoND - Disney's The Hunchback of Notre Dame - A Musical Adventure
HoP - The Hall of Presidents
HSFe - Hotel Santa Fe
IASW - "It's A Small World"
IG - International Gateway
IN - IllumiNations
JC - Jungle Cruise
JIYI - Journey Into Your Imagination
LBV - Lake Buena Vista
LOS - Length of Stay Passport
LS - The Living Seas
MGM - Disney-MGM Studios
MK - Magic Kingdom
MKC - Magic Kingdom Club
MNSSHP - Mickey's Not-So-Scary Halloween Party
MS - Main Street USA
MS - Mission:SPACE
MSEP - Main Street Electrical Parade
MV3D - Jim Henson's Muppet*Vision X3D 4D
MVMCP - Mickey's Very Merry Christmas Party
NBC - Newport Bay Club
NoJ - Night of Joy
NOS - New Orleans Square
OKW - Disney's Old Key West Vacation Club Resort
OPR - Old Port Royale (at Disney's Caribbean Beach Resort)
PH - Planet Hollywood (part of Downtown Disney)
PI - Pleasure Island (part of Downtown Disney)
PO - Disney's Port Orleans Resort, now Port Orleans French Quarter
PoC - Pirates of the Caribbean
POFQ - Port Orleans French Quarter
Poly - Disney's Polynesian Resort
PotC - Pirates of the Caribbean
RC - River Country
RC - Rainforest Cafe
SE - Spaceship Earth
SL - Sequoia Lodge
SM - Splash Mountain
SM - Space Mountain
SplM - Splash Mountain
ST - Star Tours
ST - Disney-MGM Studios
TDS - The Disney Store
TL - Typhoon Lagoon
TLS - The Living Seas
TM - Big Thunder Mountain Railroad
TMK - Magic Kingdom
ToT - "The Twilight Zone Tower of Terror"
TS - Ticket Services
TSI - Tom Sawyer Island
TST - Disney-MGM Studios
TT - Test Track
TTA - Tomorrowland Transit Authority
TTC - Transportation and Ticket Center
TZToT - "The Twilight Zone Tower of Terror"
UoE - Universe of Energy
UMP - Unlimited Magic Pass, now UPH, Unlimited Park Hopper
VM - Disney Village Marketplace (part of Downtown Disney)
VMCP - Mickey's Very Merry Christmas Party
VotLM - Voyage of the Little Mermaid
WDW - Walt Disney World Resort
WL - Disney's Wilderness Lodge Resort
WLV - Wilderness Lodge Villas
WoD - Disney's World of Disney
WoL - Wonders of Life
WoM - World of Motion
WS - World Showcase (part of Epcot)
WS - West Side (part of Downtown Disney)
WWoS - Disney's Wide World of Sports
WWS - Disney's Wide World of Sports
Y&B - Disney's Yacht Club Resort and Disney's Beach Club Resort
YC - Disney's Yacht Club Resort
20K - Twenty-thousand Leagues Under the Sea
Disney Newsgroup abbreviations:
add - alt.disney.disneyland
add(l) - alt.disney.disneyland
add(w) - alt.disney.disneyworld
DDD - Disney Deprivation Disorder
FDC - Future Disney Cabinet
RAD - rec.arts.disney
r.a.d. - rec.arts.disney
r.a.d.* - rec.arts.disney (all three tend to refer to the entire cluster of Disney related newsgroups here in the rec.* hierarchy)
RADP - rec.arts.disney.parks
radp - rec.arts.disney.parks
r.a.d.parks - rec.arts.disney.parks
RAD.p - rec.arts.disney.parks
TDC - Trimobious Disney Cabinet
WDWIG - Deb's Unofficial Walt Disney World Information Guide
Other common abbreviations (this list doesn't have *all* the abbreviations)
BTW - By The Way
FWIW - for what it's worth
IMHO - in my humble opinion
OT - off topic
OTOH - On the Other Hand
ROFL - rolling on floor laughing
ROFLMAO - rolling on floor laughing my *butt* off
TTFN - Ta Ta For Now
TTYL - Talk To You Later
YMMV - Your Mileage May Vary (means that no two people experience the same thing in exactly the same way, just a caution placed on some descriptions of places, events, food, merchandise, consumer habits, practices, etc.)
A Couple of Notes
GOH or GoH - Guest of Honor, parodying and imitating WDW's practice this year of honoring which year park visitors visited WDW for the first time. Some people added this information, speaking about themselves, in their signatures at the bottoms of posts. It simply means the year the person writing the posting to the newsgroup visited WDW for the first time.
Emoticons - Emoticons: Punctuation signs that are arranged within text in such a way as to display the simulation of a face when viewed by turning your head to one side. Inserted into text to relay a facial expression or emotion/attitude to match the text, softens the text to "humanize" it somewhat and make it seem less harsh, less blunt, offered as friendly advice, etc., or to relay how news/information affects the writer.
:-) or

- Happy/smiling
:-( or :-( - Sad/frowning/disappointment

- Very happy/Very big grin
:-/ - Skepticism/not feeling great
;-) or

- Winking and smiling/in-joke or joking or teasing
:-| - Ambivalence/Not pleased
()_() ()~()
(_) (_)
Mickey and Minnie Mouse, respectively, the leaders of the Club that's made for you and me!