• Adenomatous hyperplasia – cf. endometrial adenomatous hyperplasia and atypical adenomatous hyperplasia
• Ah (digraph)
• After-hours trading
  Extended hours trading
  After-hours trading is stock trading that occurs after the traditional trading hours of the major exchanges, such as the New York Stock Exchange and the Nasdaq Stock Market. Since 1985, the regular trading hours in America have been from 9:30 a.m. to 4:00 p.m...
  
   in stock trading
• Adolf Hitler
  Adolf Hitler
  Adolf Hitler was an Austrian-born German politician and the leader of the National Socialist German Workers Party , commonly referred to as the Nazi Party). He was Chancellor of Germany from 1933 to 1945, and head of state from 1934 to 1945...
  
  
• Air handler
  Air handler
  An air handler, or air handling unit , is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning system. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and...
  
  , Often abbreviated to AHU, is a device used to condition and circulate air
• Albert Heijn
  Albert Heijn
  Albert Heijn B.V. is a supermarket chain founded in 1887 in Oostzaan, Netherlands. It is named after Albert Heijn, Sr., the founder of the first store in Oostzaan....
  
  , a Dutch supermarket chain owned by Ahold
• Anno Hegirae (Hijri year
  Hijri year
  The Hijri year is year numbering system used in the Islamic calendar. It commemorates the Hijra , or emigration of Muhammad and his followers to the city of Medina in 622 CE. In Arabic, AH is symbolized by the letter هـ...
  
  ) in the Islamic calendar
  Islamic calendar
  The Hijri calendar , also known as the Muslim calendar or Islamic calendar , is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in many Muslim countries , and used by Muslims everywhere to determine the proper day on which to celebrate Islamic...
  
  
• Ampere-hour
  Ampere-hour
  An ampere-hour or amp-hour is a unit of electric charge, with sub-units milliampere-hour and milliampere second...
  
  , a unit of electric charge.
• Anhui
  Anhui
  Anhui is a province in the People's Republic of China. Located in eastern China across the basins of the Yangtze River and the Huai River, it borders Jiangsu to the east, Zhejiang to the southeast, Jiangxi to the south, Hubei to the southwest, Henan to the northwest, and Shandong for a tiny...
  
  , a Chinese province
• an attohenry, from the Henry (unit), an SI unit of inductance
• Auction house
• Austria–Hungary, a former European empire

In aviation:

• AH-1 Cobra
  AH-1 Cobra
  The Bell AH-1 Cobra is a two-bladed, single engine attack helicopter manufactured by Bell Helicopter. It shares a common engine, transmission and rotor system with the older UH-1 Iroquois...
  
  , a model of attack helicopter
• AH-64 Apache
  AH-64 Apache
  The Boeing AH-64 Apache is a four-blade, twin-engine attack helicopter with a tailwheel-type landing gear arrangement, and a tandem cockpit for a two-man crew. The Apache was developed as Model 77 by Hughes Helicopters for the United States Army's Advanced Attack Helicopter program to replace the...
  
  , a model of attack helicopter
• Artificial Horizon, a cockpit instrument (Aviation)

In computing:

• Ah (computer virus)
  Ah (computer virus)
  Ah is a very buggy computer virus which infects COM files including command.com. Ah is based on the V1024 virus, and originated in Italy in May 1991. When the first program infected with Ah is executed, Ah will install itself memory resident at the top of system memory, but below the 640K DOS...
  
  
• AH register, the high byte of an X86 16-bit AX register
• Authentication Header, a part of the IPsec protocol suite

In entertainment:

• A-ha
  A-ha
  A-ha were a Norwegian pop band formed in Oslo in 1982. The band was founded by Morten Harket , Magne Furuholmen , and Pål Waaktaar...
  
  , a New Wave/Synthpop band from Norway
  Norway
  Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
  
  
• Alternate History, a subgenre of speculative fiction
• Arcana Heart
  Arcana Heart
  is a 2D arcade fighting game series developed by Examu Inc. . The first edition was released to arcades in late 2006...
  
  . a video game series
• Avalon Hill
  Avalon Hill
  Avalon Hill was a game company that specialized in wargames and strategic board games. Its logo contained its initials "AH", and it was often referred to by this abbreviation. It also published the occasional miniature wargaming rules, role-playing game, and had a popular line of sports simulations...
  
  , makers of military-themed board games