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Adaptive Transform Coding, a method of coding for speech signals

Adari Tele Comp, Application hosting and Development services.

Agreement on Textiles and Clothing

Air traffic control

Air Traffic Controller Climbing Belay Device

Air Training Command, the predecessor to Air Education and Training Command of the United States Air Force

Air Training Corps

Air Training Corps (New Zealand)

ALCOA Technical Center

All-terrain (motor)cycle — see all-terrain vehicle

All Things Considered, a news show on National Public Radio in the United States.

American Thermoplastic Company

American Turkish Council

Anatomical Therapeutic Chemical Classification System for drugs (WHO).

Aquarian Tabernacle Church

Argentina Televisora Color Argentina's state-owned TV station.

Artist trading cards

Asia and The Pacific Ocean Trade Center

ATC, A Touch of Class, the pop music group from Germany

ATC, a proprietary belay device used in climbing

Athletic Trainer Certified

Atlanta Transit Company was in operation from 1950 to 1972

Audio Tele-Conference or Conference call

Austin (Texas) Technology Council

Austin Title Company

Australian Telecommunications Commission, which was later renamed to the Australian Telecommunications Corporation

Automatic traction control

Automatic Train Control

Average total cost

Anatomical Therapeutic Chemical Classification System for Human Medicines (ATC)

Autodesk Authorised Training Centre