Aviation

• AAD, IATA airport code for Ad-Dabbah Airport in Ad-Dabbah, Sudan
• AAD, ICAO airline designator for Aero Aviation Centre Ltd. in Canada
• Automatic activation device
  Automatic activation device
  Automatic Activation Device in skydiving terminology refers to an electronic-pyrotechnic or mechanical device that automatically opens the main or reserve parachute container at a preset altitude or after a preset time....
  
  , a "fail-safe" device often used in a parachute pack

Clubs and organizations

• Ad Altare Dei, a Boy Scouts of America award; see Religious emblems programs (Boy Scouts of America)

Education

• Australian Academy of Design
  Australian Academy of Design
  The Australian Academy of Design is a not-for-profit private school of design based in Port Melbourne. A Government-recognised Higher Education Provider , it is one of only two Australian higher education institutions to deliver a Bachelor of Design Arts, and offers major studies in Advertising,...
  
  , an art and design college based in Melbourne, Australia

Mathematics

• average absolute deviation in statistics, a way to report error against reference data

Medicine

• American Academy of Dermatology
  American Academy of Dermatology
  The American Academy of Dermatology is the largest organization of dermatologists in the world. It was founded in 1938 and represents 17,000 dermatologists in the United States, Canada, and around the world. The Academy grants Fellowships and Associate Memberships, as well as Fellowships for...
  
  
• Antibiotic-associated diarrhea
  Antibiotic-associated diarrhea
  Antibiotic-associated diarrhea results from an imbalance in the colonic microbiota caused by antibiotic therapy. Microbiota alteration changes carbohydrate metabolism with decreased short-chain fatty acid absorption and an osmotic diarrhea as a result...
  
  
• 7-Aminoactinomycin D (7-AAD), a fluorescent stain for DNA
• Acute Aortic Dissection, see Aortic dissection
  Aortic dissection
  Aortic dissection occurs when a tear in the inner wall of the aorta causes blood to flow between the layers of the wall of the aorta and force the layers apart. The dissection typically extends anterograde, but can extend retrograde from the site of the intimal tear. Aortic dissection is a medical...
  
  

Government, Political

• Associação de Activismo para a Democracia, a political party active during the Macanese legislative election, 2009
  Macanese legislative election, 2009
  Legislative elections were held in Macau on 20 September 2009. The official campaign began on 5 September, and several candidates received warnings from the Electoral Affairs Commission for having begun campaign activities beforehand....
  
  
• Australian Antarctic Division
  Australian Antarctic Division
  The Australian Antarctic Division is an agency of the Department of Sustainability, Environment, Water, Population and Communities . The division undertakes science programs and research projects to contribute to an understanding of Antarctica and the Southern Ocean...
  
  , which manages Australia's four Antarctic/sub-Antarctic stations, as well as Heard Island

Military

• Advanced Air defense, anti-ballistic missile in the Indian Ballistic Missile Defense Program
  Indian Ballistic Missile Defense Program
  The Indian Ballistic Missile Defense Program is an initiative to develop and deploy a multi-layered ballistic missile defense system to protect India from ballistic missile attacks....
  
  

Technology

• aad, or "ASCII Adjust before Division", an Intel BCD opcode
• AAD, code for a CD that was recorded analog, mixed analog, and transferred digitally; see SPARS code
  SPARS Code
  SPARS is an acronym for the Society of Professional Audio Recording Services. The SPARS code is a three-letter code that appears on some Compact Disc recordings telling the consumer whether analog or digital equipment was used in producing the recording...