All articles starting with O
9,097 articles
Opportunistic osteoporosis screening
Opportunistic osteoporosis screening identifies low bone mineral density and vertebral fractures on CT scans already acquired for unrelated reasons, adding no cost, time, or radiation.
Opportunistic relaying
Opportunistic relaying is a cooperative wireless communication technique that selects the single best relay from several candidates using local channel measurements, achieving diversity gains on the order of the number of relays without multi-relay coordination.
Opportunistic salpingectomy
Opportunistic salpingectomy is the removal of both fallopian tubes during a pelvic operation a woman is already having, to prevent ovarian cancer without causing menopause.
Opportunistic sampling
Opportunistic sampling is a form of nonprobability sampling that collects data from readily available sources, such as citizen-science records and museum specimens, rather than by a known random mechanism.
Opportunistic scheduling
Opportunistic scheduling is a wireless network technique that assigns each time slot to the user whose channel conditions are momentarily best, exploiting multiuser diversity to raise total throughput.
Opportunistic spectrum access
Opportunistic spectrum access is a spectrum-sharing model in which unlicensed secondary users transmit in radio bands that licensed users are not using, exploiting temporarily vacant channels.
Opportunistic Wireless Encryption
Opportunistic Wireless Encryption (OWE) is a Wi-Fi security method that encrypts open networks without authentication, specified in RFC 8110 in 2017 and certified as Enhanced Open.
Opportunity (rover)
Opportunity, nicknamed Oppy, was a NASA Mars rover that landed in 2004 and found evidence of ancient water, operating for nearly 15 years against a planned 90-day mission.
Opportunity charging
Opportunity charging is recharging battery-electric vehicles with short, high-power top-ups during dwell times already built into their schedules, at stops or termini, letting buses and trucks use smaller batteries.
Opportunity cost
Opportunity cost, also called alternative cost, is the value of the next-highest-valued alternative use of a resource given up when a choice is made, a direct consequence of scarcity.
Opportunity Knocks (British TV series)
Opportunity Knocks was a British radio and TV talent show hosted by Hughie Green from 1949, using a clapometer and postal public vote; ITV 1956–1978, BBC revival 1987–1990 with Bob Monkhouse and Les Dawson.
Opportunity Party (Albania)
Opportunity Party (Partia Mundësia), Albanian centre-right anti-corruption party founded 2024 by Agron Shehaj as a Democratic Party spin-off; won 2 of 140 parliamentary seats and 48,995 votes in its first contest, the May 2025 election.
Opposed-piston engine
An opposed-piston engine is an internal combustion engine in which two pistons share each cylinder, moving in opposite directions with the combustion chamber between them and no cylinder head.
Opposing force
An opposing force (OPFOR), also known as OpFor, is a military unit tasked with representing an enemy, usually for training purposes in war game scenarios and at combat training centers.
Opposite Sex (TV series)
Opposite Sex is a 2000 Fox comedy-drama about three boys, including Chris Evans and Milo Ventimiglia, enrolled at a formerly all-girls school; created by Abby Kohn and Marc Silverstein, canceled after 8 episodes.
Opposition frontbench of Kemi Badenoch
Kemi Badenoch's opposition frontbench: the three Conservative shadow cabinets (November 2024, July 2025, August 2026 reshuffle) she formed as Leader of the Opposition, their members, reshuffles, and staffing constraints.
Opposition Platform — For Life (Опозиційна платформа — За життя)
Opposition Platform — For Life (Опозиційна платформа — За життя, OPZZh): pro-Russian Ukrainian party registered 1999 as Center, formed in 2018 under Rabinovich, Boyko, and Medvedchuk; placed second in the 2019 parliamentary election with 13.05% and 43 seats; suspended in March 2022 and definitively banned by Ukraine's Supreme Court on 15 September 2022.
Opposition to AI data centers
Opposition to AI data centers is the U.S. grassroots and political backlash against AI-serving facilities, over electricity bills, water use, noise, tax breaks, and few jobs, producing moratoria, bans, Gallup majorities, and state legislation.
Opposition to immigration
Opposition to immigration: attitudes, movements, and policies favoring reduced migration. Spans U.S. nativism (Know-Nothings, Chinese Exclusion Act 1882, 1924 quota act), eugenics-linked restrictionism, and modern UK, French, and U.S. public opinion and enforcement politics.
Opposition to the overthrow of the Hawaiian Kingdom
Opposition to the overthrow of the Hawaiian Kingdom: Native Hawaiian resistance after the January 17, 1893 coup against Queen Liliʻuokalani, including the 1895 Wilcox Rebellion, the 21,269-signature Kūʻē Petitions of Hui Aloha ʻĀina, and Senate lobbying that defeated the 1897 annexation treaty.
Opposition to United States involvement in the Vietnam War
Opposition to United States involvement in the Vietnam War (the Vietnam antiwar movement) was American dissent from 1965 to 1973: SDS marches, teach-ins, draft resistance, GI mutinies, Kent State, and an estimated 6 million dissenting Americans by the Paris Peace Accords.
Opposition to World War I
Opposition to World War I: religious, political, and labor resistance to the 1914-1918 war, including conscientious objection under conscription in Britain, New Zealand, and the US, socialist and women's antiwar activism, and wartime repression under the Espionage and Sedition Acts.
Opposition-based learning
Opposition-based learning is a machine intelligence technique that pairs each candidate solution with its opposite point in the search space, keeping the fitter to speed convergence.
Oppositional defiant disorder
Oppositional defiant disorder (ODD), also called oppositional disorder, is a childhood behavior disorder of angry, argumentative, defiant, and vindictive behavior toward authority figures lasting at least 6 months, treated mainly with parent management training and CBT.
Oppositions
Oppositions was an American architectural journal published in New York by the Institute for Architecture and Urban Studies from 1973 to 1984, in 26 issues.
Oppression
Oppression: the systematic, unjust constraint or reduction of a group through social forces. Covers Young's five faces, Frye's enclosing structures, structural operation, and 2021 ILO count of 49.6 million in modern slavery.
OPQRST
OPQRST is a mnemonic used in emergency medicine, nursing, and prehospital care to structure the history of a patient's pain, covering Onset, Provocation, Quality, Region, Severity, and Time, and taught alongside SAMPLE.
OPR-1000
The OPR-1000, originally called the Korean Standard Nuclear Power Plant (KSNP), is a South Korean 1,000 MWe two-loop pressurized water reactor developed from 1984 to 1999.
Oprah Winfrey
Oprah Winfrey (Oprah Gail Winfrey, born 1954, Kosciusko, Mississippi) is an American talk show host, media executive, and philanthropist; The Oprah Winfrey Show (1986-2011) was the highest-rated talk show in history, and she became the first Black woman on the Forbes billionaire list in 2003.
Oprah Winfrey Network
Oprah Winfrey Network (OWN) is a US cable channel launched January 1, 2011, a joint venture of Harpo and Warner Bros. Discovery that replaced Discovery Health, struggled early, and turned profitable in 2013.