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Two-step task
The two-step task is a two-stage decision-making paradigm introduced by Daw and colleagues in 2011, the standard way to distinguish model-based from model-free reinforcement learning in human behavior.
Two-stream approximation
The two-stream approximation, introduced by Arthur Schuster in 1905, simplifies radiative transfer into upward and downward fluxes, enabling fast calculations in climate and exoplanet atmosphere models.
Two-stream instability
The two-stream instability, also known as the bump-on-tail instability, is a plasma instability where two drifting particle populations or a beam drive exponentially growing electrostatic waves.
Two-streams hypothesis
Two-streams hypothesis: primate visual cortex model with a ventral "what" stream to temporal cortex for perception and a dorsal "where/how" stream to parietal cortex for action; proposed by Ungerleider and Mishkin (1982) and Goodale and Milner (1992), now revised toward interacting streams.
Two-stroke diesel engine
A two-stroke diesel engine is a compression-ignition engine that completes its cycle in two piston strokes, one crankshaft revolution; large low-speed versions propel most commercial ships.
Two-stroke engine
A two-stroke engine, also called a two-cycle engine, is an internal combustion engine completing its cycle in two piston strokes, giving high power-to-weight ratios and high emissions.
Two-Tax System in the Five Dynasties
The Two-Tax System in the Five Dynasties (五代两税) was the Five Dynasties and Ten Kingdoms reshaping of the Tang two-tax law, collected in summer and autumn installments.
Two-terminal tandem
A two-terminal tandem, or 2T tandem, is a tandem solar cell with two series-connected subcells accessed through two terminals; perovskite/silicon devices have reached a certified 33.7% efficiency.
Two-tier local government in England
Two-tier local government in England: county councils and district or borough councils sharing services in the same area, created by the 1972 Act, now covering 21 shire counties and about 20 million people, and being replaced by unitary authorities.
Two-tier policing
Two-tier policing: UK political accusation that police treat right-wing or white groups more harshly than progressive or minority ones; rooted in 1990s Northern Ireland policing theory, rejected by UK committees and police as evidence-free.
Two-toed amphiuma
Two-toed amphiuma (Amphiuma means), also called Congo eel or ditch eel: a large eel-like aquatic salamander of the southeastern US Coastal Plain, up to 117 cm, with two toes per foot, nocturnal ambush predator, IUCN Least Concern.
Two-tower array
A two-tower array is the simplest directional antenna system in AM broadcasting, using two towers with controlled currents to place a null in one direction.
Two-up
Two-up (swy) is a traditional Australian coin-tossing gambling game, first recorded 1854, tied to Anzac Day and WWI diggers; two heads wins, two tails loses, legal only on Anzac Day in most of Australia.
Two-way analysis of variance
Two-way analysis of variance, or two-way ANOVA, is a statistical method for testing how two factors each with multiple levels affect a response, including interactions between them.
Two-way contract
NBA two-way contract: a 2017 CBA contract type letting a player serve both an NBA team and its G League affiliate; one or two seasons, 50% of the zero-year minimum salary, up to three per team since 2023-24.
Two-way radio
A two-way radio is a transceiver that sends and receives voice or data over radio, usually in half-duplex push-to-talk mode, used in land mobile, public-safety, and license-free services such as FRS and PMR446.
Two-way ranging (UWB)
Two-way ranging (TWR) is a distance-measurement technique used in ultra-wideband (UWB) positioning, in which two transceivers exchange timestamped packets and distance comes from the round-trip time of flight, requiring no clock synchronization.
Two-way relay channel
The two-way relay channel (TWRC) is a communication model in which two terminal nodes exchange information through a common relay node, using network coding to roughly halve the spectral cost.
Two-way satellite time and frequency transfer
Two-way satellite time and frequency transfer (TWSTFT) compares atomic clocks at distant labs by exchanging signals via a geostationary satellite, a key technique for UTC.
Two-week eclipse and portent records of King Yi's reign
The two-week eclipse and portent records of King Yi's reign (懿王时天再旦) record a "double dawn" at Zheng, read as the sunrise eclipse of 21 April 899 BC.
Two's complement
Two's complement is the standard binary representation of signed integers, where negation flips all bits and adds 1, and it has a single representation of zero.
Twofish
Twofish is a symmetric block cipher published in 1998 by Bruce Schneier and colleagues, one of five finalists in the competition that produced the Advanced Encryption Standard.
Twomad
Twomad, real name Muudea Sedik (2000-2024), was a Canadian YouTuber and streamer of Ethiopian descent known for Overwatch meme montages, zoombombing, and 21st century humor memes; he died in Los Angeles of an accidental morphine overdose.
Twórczość
Twórczość (Polish for "Creation") is a Polish monthly literary and critical magazine founded in Kraków in 1945, making it the oldest Polish literary periodical still published.
TwoSet Violin
TwoSet Violin, Australian classical music comedy duo of violinists Brett Yang and Eddy Chen; YouTube channel with Ling Ling jokes, B²TSM farewell, 2024 hiatus, and 2025/26 Sacrilegious Games world tour return.
Twosret
Twosret, also spelled Tausret or Tawosret, was a female pharaoh of ancient Egypt, the last ruler of the 19th Dynasty, who reigned about 1191–1185 BC.
TWS (투어스) (group)
TWS (투어스), short for TWENTY FOUR SEVEN WITH US, is a six-member K-pop boy group under Pledis Entertainment (HYBE) that debuted January 22, 2024 with Sparkling Blue and "plot twist", Pledis's first boy group in nine years since SEVENTEEN.
TWT amplifier
A TWT amplifier (TWTA) is a high-power microwave amplifier built around a traveling-wave tube, a vacuum device offering high gain over wide bandwidths, dominant in satellite communications and radar.
Twyfelfontein or /Ui-//aes
Twyfelfontein or /Ui-//aes, a rock engraving site in Damaraland, Kunene Region, Namibia; Afrikaans for "doubtful spring". Namibia's first World Heritage Site (2007), with over 2,000 San-era petroglyphs.
Twyford
Twyford, an English placename meaning 'double ford' from Old English, borne by villages in Hampshire, Buckinghamshire, Berkshire, and West Twyford, London; the Hampshire village hosts the scheduled Twyford Roman villa, occupied from the late 1st to the 5th century.