ATM is an initialism with the following meanings:

• Adobe Type Manager, font management software from Adobe Systems
• Advanced Traffic Management and Arterial Traffic Management , terms used in the intelligent transportation system industry
• Air Traffic Management , or Air Traffic Control
• Amateur telescope making
• Asynchronous Transfer Mode, a telecommunications protocol
• At-the-money, a term used in option pricing
• Ataxia telangiectasia mutated (molecuar and cell biology, biochemistry), is a protein kinase that plays a critical role in reponse to certain types of DNA damage
• Automatic teller machine or automated teller machine, a cash dispenser
• At the moment , commonly used Internet slang
• ATM is a Russian clone of the ZX Spectrum

Also, atm. is an abbreviation for atmosphere, a unit of atmospheric pressure.