Walt Disney World a/k/a WDW has its own language amongst those that frequent it. Here are some common terms and acronyms that you may hear.
ADR: Dining reservation
CM: Cast Member (Disney-speak for employee)
CS: Counter Service restaurant (used interchangeably with Quick Service)
DAK: Animal Kingdom
Dark Ride: the term "dark ride" refers broadly to attractions where you're in a ride vehicle of some sort and you pass through various show scenes that tell a story. They are not necessarily dark.
DHS: Hollywood Studios
ECV: Electronic Conveyance Vehicle (the mobility scooters)
F&G: Epcot Flower & Garden Festival
F&W: Epcot Food & Wine Festival
FotA or FArts: Epcot Festival of the Arts
FP or FP+: technically refers to FastPass, the legacy ride-reservations system, still colloquially used to refer to Lightning Lane and Individual Lightning Lane reservations.
GR/GS: Guest Relations/Guest Services (basically customer service)
ILL: Individual Lightning Lane
LL: Lightning Lane
M&G: Meet and Greet or Character meeting
MDE/MDX: My Disney Experience (and/or the associated app)
MK: Magic Kingdom
QS: Quick Service restaurant (used interchangeably with Counter Service)
Rope Drop: Park opening
TS: Table Service restaurants, i.e., traditional restaurants where you sit down and are waited on by a server
Additionally, hotels are commonly referred to by their initials. For example, AoA refers to Art of Animation, AKL refers to Animal Kingdom Lodge, and CSR refers to Coronado Springs Resort. Similarly, obvious acronyms are used for most attractions, i.e., IASW refers to it's a small world, and CoP refers to Carousel of Progress.
I wanted to flag two other common abbreviations, both of which are specific to Disneyland, in Anaheim, California.
DCA: Disney's California Adventure
DLR: refers generally to the Disneyland Resort in Anaheim
Again, these have nothing to do with Walt Disney World, but they often pop up in Disney discussions, so I'm calling them to your attention so you understand what they are.