T3 or T-3 may refer to:

• T3: Alliance, an investigative-public affairs TV program in the Philippines
• T3 (magazine), focusing on new and hi-tech gadgets
• Terminator 3: Rise of the Machines, the third film in the Terminator series
• Tekken 3, a 1997 fighting game in the Tekken franchise
• Tiger 3, a 2023 Indian action thriller film in the YRF Spy Universe

• Fletcher's Ice Island or T-3, an iceberg and scientific research station
• T3 (skyscraper), an office building in Taichung, Taiwan
• Tokyo Teleport Town, a planned city on Odaiba, reclaimed land in Tokyo Bay

• Axiom T3, or T3 space, regular space in topology and related fields of mathematics
• T3 Technion Technology Transfer, the technology transfer office of the Technion Israel Institute of Technology
• T3 line, or Digital Signal 3, a 44.736 Mbit/s telecommunications channel standard
• T-3, a Palomar–Leiden survey Jupiter Trojan subproject
• A tornado intensity rating on the TORRO scale

• SPARC T3, a CPU introduced by Sun Microsystems in 2010
• Tungsten T3, a palmOne handheld device
• Talking tactile tablet, a touch sensitive device for visually impaired people
• Canon EOS Rebel T3, a digital camera
• T3, a Hospedia bedside television
• Sony Xperia T3, an Android smartphone

• T₃, in endocrinology, triiodothyronine, a thyroid hormone
• T3 spinal nerve
• Third thoracic vertebrae
• An electrode site in the 10–20 EEG system

• Eastern Airways (IATA code)
• Île-de-France tramway Line 3, in Paris
• T3 Bankstown Line, a former rail service in Sydney, Australia
• Liverpool & Inner West Line, a rail service in Sydney, Australia numbered T3
• T3 transit lane, a type of high-occupancy vehicle lane in Australia
• T3 road (Tanzania)
• T3 road (Zambia)
• T3 (Tram İzmir), a tram line in Turkey
• Heathrow Terminal 3

• Fuji T-3, a Japanese primary military trainer aircraft
• T3, a model of the Oslo Metro OS T1000 train
• Tatra T3, a tramcar
• Trager-Bierens T-3 Alibi, a glider
• Volkswagen Type 2 (T3), the third generation of the Volkswagen Transporter van
• T3 tanker, a ship class
• T-3 Firefly, a former US Air Force training aircraft

• T3, a halogen light bulb form factor
• T3 (company), a woman-owned advertising agency in the US
• T3 (rapper) (active beginning in 1996), founding member of the band Slum Village
• T3, a privatisation offering of the company Telstra
• T3 (roller coaster), at Kentucky Kingdom
• Tikka T3, a Finnish bolt-action rifle series
• T+3, "trade date plus three days" in financial markets

• Polar T₃ syndrome, low levels of that hormone in polar explorers
• 3T (disambiguation)
• TTT (disambiguation)