May not be a comprehensive list.

AAS Alternate Air Source, such as a pony bottles
AAUS American Academy of Underwater Sciences
ABJ Adjustable Buoyancy Jacket
ABLJ Adjustable Buoyancy Life Jacket
ABT Actual Bottom Time
ADT Actual Dive Time
AEDU Admiralty Experimental Diving Unit
AGE Arterial Gas Embolism; bubble causing obstruction to a blood vessel
AI Assistant Instructor
AMDT Adjusted Maximum Dive Time
ANDI American Nitrox Divers Incorporated
AODC Association of Offshore Diving Contractors
AOW Advanced Open Water certification; second level of PADI certification
AP Absolute Pressure
ASD Atrial Septal Defect; a hole in the heart
ASF Australian Speleological �Federation�
ASL American Sign Language
ATEA Amphibian Tank Escape Apparatus
ATA Atmospheres Absolute; absolute pressure.
ATS Atmospheres Absolute Over Sea Level (ie gauge pressure)
AUF Australian Underwater Federation
AV Artificial Ventilation
BC Buoyancy Compensator
BCD Buoyancy Control Device
BCRA British Cave Research Association
BIBS Built-In Breathing System
BPR Back Pressure Regulator
BSAC British Sub-Aqua Club
BT Bottom Time; definition is agency dependent
BWRAF PADI training acronym; "Begin with Review And Friend"
CAPS Cave mapping software & electronic survey equipment
CAUS Canadian Association for Underwater Sciences
CCBA Closed Circuit Breathing Apparatus
CDAA Cave Diving Association of Australia
CDG Cave Divers Group of Great Britain
CESA Controlled Emergency Swimming Ascent
CFT Comhairle F�-Thionn - The official name of the Irish Underwater Coucil CIRSS Comitato Italiano Ricerche Studi Subacquei (Italy)
CM Cutis Marmorata; inflamation of the skin signaled by a reddish, mottled discoloration
CMAS Confederation Mondiale des Activiti�s Subaquatiques (World Underwater Assoc)
CNS Central Nervous System
CPR Cardio-Pulmonary Resuscitation
CPS Commission Plongee Souterraine
CPTD Cummulative Pulmonary Toxic Dose
CSAC Canadian Sub-Aqua Club
DAN Diver's Alert Network
DCAP Decompression Computation and Analysis Program
DCIEM Defence and Civil Institute of Environmental Medicine
DCI Decompression Illness; including DCS and AGE
DCS Decompression Sickness; the 'bends'
DDC Deck Decompression Chamber
DDRC Diving Disease Research Center, in Plymouth, England. The leading hyperbaric treatment & research center in Britain.
DEMA Diving Equipment Manufacturers Association
DES Divers' Environmental Survey
DIN Deutsches Institut fuer Normung
DIR Term invented by George Irvine III to describe the practices that he and others derived from Hogarthian principles.
DM Dive Master
DMAC Diving Medical Advisory Committee
DO Dysbaric Osteonecrosis
DO Diving Officer
DPV Diver Propulsion Vehicle
DSEA Davis Submerged Escape Apparatus
DSMB Delayed Surface Marker Buoy; SMB which is inflated at the end of a dive
DUI Diving Unlimited International; manufacturer best known for their dry suits.
DV Demand Valve; usually the second stage of a regulator
EAD Equivalent Air Depth; The depth at which air would cause as much decompression obligation as nitrox with a given fO2 at a given depth
EAN Enriched Air Nitrox
EANx Enriched Air Nitrox
EAR Expired Air Resuscitation (preferred term in Britain is now AV)
EATD European Association of Technical Divers
EAV Expired Air Ventilation
EBS Emergency Breathing System
ECC External Cardiac Compression
ECU Environmental Control Unit
END Equivalent Narcotic Depth; depth at which air would cause as much narcosis as a given mix and depth
FAUI Federation of Australian Underwater Instructors
FFA Feet First Ascent; common problem for new dry suit users
FFDS Federation Francais De Speleologie
FFM Full Face Mask
FFW Feet of Fresh Water
FGV Free Gas Volume
fHe Fraction of Helium in a gas mixture
fN2 Fraction of Nitrogen in a gas mixture
fO2 Fraction of Oxygen in a gas mixture
FPS Foot, Pound, Second (Imperial System)
FSW Feet of Salt Water
FV Floodable Volume
GPS Global Positioning System
HP High Pressure
HPNS High Pressure Nervous Syndrome
HSA Handicapped Scuba Association
HSE Health and Safety Executive
IAND International Association of Nitrox Divers
IANTD International Association of Nitrox and Technical Divers
IDEA International Diving Educators Association
IP Intermediate Pressure; the pressure between the first and second stages of a regulator
IUC Irish Underwater Council
LAT Lowest Astronomical Tide
LP Low Pressure
MDEA Multinational Diving Educators Association
MDT Maximum Dive Time
MFW Metres of Fresh Water
MGR Mixed Gas Rebreather
MKS Metre, Kilogram, Second (Metric System)
MOD Maximum Operating Depth; maximum depth for a mix, given a maximum ppO2
MSW Metres of Salt Water
NABS National Association of Black Scuba Divers
NACD National Association for Cave Diving
NACDS National Association of Commercial Diving Specialists
NASDS National Association of Scuba Diving Schools
NAUI National Association of Underwater Instructors
NDC National Diving Council
NDL No Decompression Limit
NDO National Diving Officer
NDS No Decompression Stop; the no decompression limit according to table or computer
NDSTC Naval Dive and Salvage Training Center
NED Network of Egghead Divers
NEDU Naval Experimental Diving Unit
NERC National Environment Research Council (UK)
NOAA National Oceanic and Atmospheric Administration
NOB Nederlands Onderwater Bond
NRMI Naval Medical Research Unit
NSB Natal Shark Board
NSS-CDS National Speleological Society-Cave Diving Section
OMS Ocean Management Systems; manufacturer known for their low pressure steel tanks
OOA Out of Air
OS O.S. Systems, Inc.; manufacturer of shell dry suits
OTT Oxygen Tolerance Test
OTU Oxygen Toxicity Unit
OSHA Occupational Safety and Health Administration (USA)
OW Open Water
P Pressure
PADI Professional Association of Diving Instructors
PADUA Pennsylvania Analysis of Decompression for Undersea and Aerospace
PDC Personal Dive Computer
PDIC Professional Diving Instructors Corporation
PFO Patent Foramen Ovale; openable flap between the atria of the heart
pp Partial Pressure; total pressure of a gass mixture is the sum of the partial pressures of the component gases
ppHe Partial Pressure of Helium in a gas mixture
ppN2 Partial Pressure of Nitrogen in a gas mixture
ppO2 Partial Pressure of Oxygen in a gas mixture
PSI Pounds per Square Inch
PTC Personal Transfer Capsule
RDP Recreational Dive Planner
RG Repetitive Group
RIB Rigid Inflatable Boat; solid keel and large inflatable tubes
RMV Respiratory Minute Volume
RNT Residual Nitrogen Time
RNLI Royal National Lifeboat Institution
RNPL Royal Naval Physiological Laboratory
ROV Remotely Operated Vehicle
RSTC Recreational Scuba Training Committee
SAA Sub-Aqua Association
SAC Surface Air Consumption
SAELO Supply Activated Exhaust Cut-Off Valve
SAFE PADI training acronym; "Slowly Ascend From Every Dive"
SAR Search and Rescue
SAUU South African Underwater Union
SCBA Self-Contained Breathing Apparatus; such as Firefighter use
SCOR Scientific Committee on Oceanic Research (of International Council of Scientific Unions)
SCUBA Self-Contained Underwater Breathing Apparatus
SDC Submersible Decompression Chamber
SEBA Submarine Escape Breathing Apparatus
SGA Siebe Gorman Amphibian
SI Systeme International (Metric System)
SI Surface Interval
SIT Surface Interval Time
SLAM Scuba Lifesaving Accident Management
SLJ Surface Life Jacket
SMB Surface Marker Buoy; buoy with a flag on a line to a diver
SOB Same Ocean Buddy
SPG Submersible Pressure Guage
SPUMS South Pacific Underwater Medical Society
SRT Single Rope Technique
SSAC Scottish Sub-Aqua Club
SSI Scuba Schools International
TDT Total Dive Time
TNT Total Nitrogen Time
TOD Theoretical Ocean Depth
UBA Universal Breathing Apparatus
UIS Union Internationale de Speologie (International Speleological Union)
UASR Underwater Association for Scientific Research (UK)
UBMS Undersea Biomedical Society (USA)
UNCLOS United Nations Convention on the Law of the Sea
UNESCO United Nations Educational, Scientific and Cultural Organization
UPTD Unit Pulmonary Toxic Dose
USN United States Navy
USOA Underwater Society of America
VENTID Vision Ears Nausea Twitching Irritation Dizziness
VGE Venous Gas Embolism
VIP Visual Inspection Program; testing a tank for integrity by visual inspection of the insides
WKPP Woodsville-Karst Plains Project; cave diving group
WPB West Palm Beach
YMCA Young Men's Christian Association