Adult diphtheria and tetanus vaccination

Asynchronous data transfer, a method of transferring data

Abstract data type, a computer programming term

Admission, Discharge, and Transfer, a message type used in Health Level 7 formatted communication

Active Denial Technology

Autodesk Architectural Desktop, CAD software from Autodesk

ADT Security Services, a division of Tyco International, formerly American District Telegraph

Average Daily Traffic, to show the volume of traffic on a road in transportation planning

Average downtime, a simple quantification of a system's reliability

ADT is a three-letter acronym that may refer to:

Automatic double tracking, an audio recording technology invented for The Beatles

Atlantic Daylight Time

ADT College, a City Technology College in London

Apple Disk Transfer, software for exchanging floppy disk images between Apple II computers and host computers over serial links

American Discovery Trail, a coast-to-coast hiking trail across the mid-tier of the United States.