| Acronym | Definition |
|---|
| ALT | Alternative (USENET newsgroup prefix) |
| ALT | Alternate |
| ALT | Altitude |
| ALT | Alto |
| ALT | Alteration |
| ALT | Alternating |
| ALT | Association for Learning Technology |
| ALT | Alanine Aminotransferase |
| ALT | Altimeter |
| ALT | Algorithmic Learning Theory (Conference) |
| ALT | Radar Altimeter (SEASAT, GEOS-3) |
| ALT | Adult Learning and Teaching (degree program) |
| ALT | Assistant Language Teacher |
| ALT | Argon Laser Trabeculoplasty |
| ALT | Alternative |
| ALT | Adaptive Lighting Technology |
| ALT | Analogue Loopback Transfer |
| ALT | Automated Loop Test |
| ALT | Altoona Transportation Center (Amtrak station code; Altoona, PA) |
| ALT | Alanine Amino Transferase (medical) |
| ALT | Advanced Learning Technologies |
| ALT | Acquisition, Logistics, and Technology (US Army) |
| ALT | Accelerated Life Testing |
| ALT | Applied Laser Technology (various locations) |
| ALT | Alternative Lengthening of Telomeres (cells) |
| ALT | Accelerated Life Test |
| ALT | Altus AFB (Altus, OK) |
| ALT | Approach and Landing Test |
| ALT | Assistant Leader Trainer |
| ALT | Acquisition Lead Time |
| ALT | Association for Linguistic Typology |
| ALT | Allocation Logement Temporaire (French: Temporary Housing Allowance) |
| ALT | Aboriginal Lands Trust (Department of Indigenous Affairs) |
| ALT | Alliance for Lobbying Transparency (UK) |
| ALT | Administrative Lead Time |
| ALT | Airsoft Lunel Team (French Airsoft group) |
| ALT | Anarchists, Lunatics and Terrorists (apocryphal origin of newsgroup hierarchy) |
| ALT | Anti Leech Tracker |
| ALT | Achievement Level Test |
| ALT | Approximate Lower Triangular (coding scheme) |
| ALT | Association for Local Telecommunications |
| ALT | Army Liaison Team |
| ALT | Amarillo Little Theatre (Amarillo, TX) |
| ALT | Associazione per la Lotta Alla Trombosi e Alle Malattie Cardiovascolari (Italian: Association to Combat Thrombosis and Cardiovascular Disease; est. 1986) |
| ALT | Automatic Link Transfer |
| ALT | Airborne Laser Tracker |
| ALT | Advanced Lightning Technology |
| ALT | Aer Lingus Teoranta |
| ALT | Automatic Line Testing (Nortel) |
| ALT | Alanina Amminotrasferasi (Italy) |
| ALT | Active Leap Technology |
| ALT | ATM Link Termination |
| ALT | All Legal Transitions |
| ALT | Associazione Italiana per la Lotta Alla Trombosi |
| ALT | Analog Line Termination |
| ALT | Asynchronous Line Test |
| ALT | Automatic Line Thresholded |
| ALT | Alarms and Telemetry (Sprint) |
| ALT | Aljamiado Learning Technologies (est. 2001) |