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Backpropagation neural network
A backpropagation neural network is a feedforward neural network trained by backpropagation, which repeatedly adjusts weights to minimize the difference between actual and desired outputs.
Backpropagation through time
Backpropagation through time (BPTT) is the algorithm used to compute gradients in recurrent neural networks by unfolding the recurrence over time steps and applying ordinary backpropagation, as formalized by Paul Werbos in 1990.
Backreaction
Backreaction in gravitational physics is the modification of a classical spacetime geometry by quantum fields, formulated in the semiclassical Einstein equation introduced by Robert Wald in 1977.
Backronym
Backronym (bacronym): a phrase invented after the fact so its initial letters spell an existing word, coined 1983 in the Washington Post; covers mnemonics like Apgar and false etymologies like posh from "port out, starboard home."
Backrooms (film)
Backrooms, also called The Backrooms Movie, is a 2026 American horror film directed by Kane Parsons for A24, based on his YouTube series and the Backrooms creepypasta.
Backrooms (soundtrack)
Backrooms (Original Soundtrack) is the dark-ambient score album for A24's 2026 horror film Backrooms, composed by director Kane Parsons and Edo Van Breemen, released May 29, 2026 on A24 Music, 28 tracks, with licensed Boards of Canada and The Caretaker cues.
Backrooms (web series)
The Backrooms is Kane Parsons' (Kane Pixels) found-footage analog horror web series on YouTube, begun January 2022, adapting the 2019 4chan Backrooms creepypasta; it drew hundreds of millions of views and led to A24's 2026 Backrooms film.
Backscatter
Backscatter, or back-scattering, is radiation or waves scattered back toward the direction they came from, near a 180-degree scattering angle, and is measured in radar, lidar, and optics.
Backscatter communication
Backscatter communication (BackCom) is a wireless method where a device sends data by reflecting incoming radio waves, consuming so little power that battery-free tags are practical.
Backscatter X-ray
Backscatter X-ray, also known as the backscatter scan, is an imaging technique that detects X-rays scattered off an object, used for security screening of people and vehicles.
Backscattered electron imaging
Backscattered electron imaging is a scanning electron microscopy mode in which the image is formed from elastically scattered beam electrons, revealing compositional differences rather than surface topography.
Backside power delivery
Backside power delivery (BSPDN) routes a chip's power supply through the back of the silicon wafer, freeing frontside wiring; Intel deploys it as PowerVia on 18A.
Backslash
Backslash (\), officially REVERSE SOLIDUS, U+005C: mirror of the slash, used in Windows file paths (C:\path, \\server\share), as escape character in string literals, in TeX macros, and as surrogate for the set-minus operator; little used before 1961.
Backspacer
Backspacer is Pearl Jam's ninth studio album, released September 20, 2009, produced by Brendan O'Brien and named for a key on Eddie Vedder's typewriter. It debuted at No. 1 on the Billboard 200 with 189,000 first-week copies, the band's first chart-topper since No Code (1996).
Backstabbed in a Backwater Dungeon
Backstabbed in a Backwater Dungeon is a Japanese light novel series by Shisui Meikyō and illustrator tef, serialized online from 2020, with over 4.6 million copies in circulation.
Backstepping
Backstepping is a recursive nonlinear control design method, first developed in 1991, that stabilizes strict-feedback systems by building a control law and a global Lyapunov function together.
Backstrap loom
A backstrap loom, in Spanish telar de cintura, is a portable frameless loom in which the weaver supplies tension by leaning against a waist strap. Used in the Americas for over 4,000 years.
Backstreet Boys
Backstreet Boys, American pop vocal group formed in Orlando in 1993 by Lou Pearlman; members Nick Carter, Brian Littrell, AJ McLean, Howie Dorough, Kevin Richardson; best-selling boy band with over 130 million albums, famous for Millennium and I Want It That Way.
Backstreet Boys (1996 album)
Backstreet Boys (1996 album): self-titled international debut studio album of the American boy band Backstreet Boys, released May 6, 1996 in Europe and Asia; produced with Max Martin in Stockholm; basis of the 1997 US debut.
Backstreet Boys (1997 album)
Backstreet Boys (US, 1997) is the American boy band's second self-titled album, released August 12, 1997 on Jive; a 12-track US debut compiling songs from the 1996 international debut and Backstreet's Back, featuring Quit Playing Games (No. 2 Hot 100).
Backstreet Boys discography
Backstreet Boys discography: studio albums, compilations, and singles by the American pop group, from Backstreet Boys (1996 EU, 1997 US) and Millennium (1999, 24 million sold) to DNA (2019), A Very Backstreet Christmas (2022), and Millennium 2.0 (2025).
Backstreet Rookie
Backstreet Rookie (편의점 샛별이) is a 16-episode South Korean romantic comedy series that aired on SBS from June 19 to August 8, 2020, starring Ji Chang-wook and Kim Yoo-jung.
Backstroke
Backstroke: competitive swimming stroke swum on the back with alternating arms and flutter kick; only stroke started in the water; 15 m underwater limit; Olympic event since 1900.
Backstroke of the West
Backstroke of the West, full title Star War: The Third Gathers – The Backstroke of the West, is a 2005 Chinese bootleg DVD of Star Wars: Episode III – Revenge of the Sith famous for machine-translated English subtitles and the "Do Not Want" meme.
Bäckström (Swedish TV series)
Bäckström is a Swedish crime drama (2020–2024) based on Leif GW Persson's Evert Bäckström novels, starring Kjell Bergqvist; three six-episode seasons on C More/TV4, distinct from the US series Backstrom.
Backsword
The backsword, also known as the Pallasch, is a straight, single-edged sword whose thickened spine adds stiffness for cutting, typically with a basket hilt; the term also names an English fencing tradition.
Backtesting
Backtesting is a validation method that evaluates a risk model, trading strategy, or forecasting rule by applying it to historical data; in banking, it compares daily value-at-risk forecasts with actual losses.
Backtracking
Backtracking, or backtracking search, is a class of algorithms for solving constraint satisfaction problems, formalized by Golomb and Baumert in 1965 and famously applied to the eight queens puzzle.
Backtracking (solar tracking)
Backtracking is a solar tracker control strategy that rotates panels away from the sun in early morning and late afternoon so one row does not shade the next.
Backtracking line search
Backtracking line search is an optimization procedure that repeatedly multiplies a trial step length by a constant factor until the Armijo sufficient-decrease condition holds, accepting the first adequate step.