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Automated teller machine or automatic teller machine, a cash dispenser or cash machine.

Asynchronous Transfer Mode, a telecommunications protocol

Actun Tunichil Muknal, Cave in Belize

Adobe Type Manager, typeface management software from Adobe Systems

Advanced Traffic Management and Arterial Traffic Management, terms used in the Intelligent Transportation System industry

Aggregate Trailer Mass, the total mass of a fully laden Trailer (vehicle)

Air Traffic Management (includes air traffic control, air space management and air traffic flow management)

Amateur telescope making

Anti-tank guided missile

Ass to mouth, a sexual act commonly observed in pornography

Association of Teachers of Mathematics in the UK

At-the-money, a term used in option pricing

Ataxia telangiectasia mutated (in molecular and cell biology, biochemistry), a protein kinase that plays a critical role in response to certain types of DNA damage

Altamira Airport, using its IATA airport code

At the moment, often used as shorthand in on-line conversations, such as instant messaging

Atmosphere (unit), a unit of atmospheric pressure

Postnominal for people granted any of the Advanced Toastmaster awards from Toastmasters International.