Disinformation
Etymology: The English word disinformation comes from the application of the Latin prefix dis- to information making the meaning "reversal or removal of information". The rarely used word had appeared with this usage in print at least as far back as 1887. 
Some consider it a loan translation of the Russian дезинформация, transliterated as dezinformatsiya, apparently derived from the title of a KGB black propaganda department. Soviet planners in the 1950s defined disinformation as "dissemination (in
the press, on the radio, etc.) of false reports intended to mislead public opinion." 
Disinformation first made an appearance in dictionaries in 1985, specifically, Webster's New College Dictionary and the American Heritage Dictionary. In 1986, the term disinformation was not defined in Webster's New World Thesaurus or New Encyclopædia Britannica. After the Soviet term became widely known in the 1980s, native speakers of English broadened the term as "any government communication (either overt or covert) containing intentionally false and misleading material, often combined selectively with true information, which seeks to mislead and manipulate either elites or a mass audience."
By 1990, use of the term disinformation had fully established itself in the English language within the lexicon of politics. By 2001, the term disinformation had come to be known as simply a more civil phrase for saying someone was lying. Stanley B. Cunningham wrote in his 2002 book The Idea of Propaganda that disinformation had become pervasively used as a synonym for propaganda.

Operationalization: The Shorenstein Center at Harvard University defines disinformation research as an academic field that studies “the spread and impacts of misinformation, disinformation, and media manipulation,” including “how it spreads through online and offline channels, and why people are susceptible to believing bad information, and successful strategies for mitigating its impact” According to a 2023 research article published in New Media & Society, disinformation circulates on social media through deception campaigns implemented in multiple ways including: astroturfing, conspiracy theories, clickbait, culture wars, echo chambers, hoaxes, fake news, propaganda, pseudoscience, and rumors.

In order to distinguish between similar terms, including misinformation and malinformation, scholars collectively agree on the definitions for each term as follows: (1) disinformation is the strategic dissemination of false information with the intention to cause public harm; (2)  misinformation represents the unintentional spread of false information; and (3) malinformation is factual information disseminated with the intention to cause harm, these terms are abbreviated 'DMMI'.
In 2019, Camille François devised the "ABC" framework of understanding different modalities of online disinformation: 

Manipulative Actors, who "engage knowingly and with clear intent in viral deception campaigns" that are "covert, designed to obfuscate the identity and intent of the actor orchestrating them." Examples include personas such as Guccifer 2.0, Internet trolls, state media, and military operatives.
Deceptive Behavior, which "encompasses the variety of techniques viral deception actors may use to enhance and exaggerate the reach, virality and impact of their campaigns." Examples include troll farms, Internet bots, astroturfing, and "paid engagement".
Harmful Content, which includes health misinformation, manipulated media such as deepfakes, online harassment, violent extremism, hate speech or terrorism.
In 2020, the Brookings Institution proposed amending this framework to include Distribution, defined by the "technical protocols that enable, constrain, and shape user behavior in a virtual space". Similarly, the Carnegie Endowment for International Peace proposed adding Degree ("distribution of the content ... and the audiences it reaches") and Effect ("how much of a threat a given case poses").

Comparisons with propaganda: Whether and to what degree disinformation and propaganda overlap is subject to debate. Some (like U.S. Department of State) define propaganda as the use of non-rational arguments to either advance or undermine a political ideal, and use disinformation as an alternative name for undermining propaganda. While others consider them to be separate concepts altogether. One popular distinction holds that disinformation also describes politically motivated messaging designed explicitly to engender public cynicism, uncertainty, apathy, distrust, and paranoia, all of which disincentivize citizen engagement and mobilization for social or political change.

Practice: Disinformation is the label often given to foreign information manipulation and interference (FIMI). Studies on disinformation are often concerned with the content of activity whereas the broader concept of FIMI is more concerned with the "behaviour of an actor" that is described through the military doctrine concept of tactics, techniques, and procedures (TTPs).
Disinformation is primarily carried out by government intelligence agencies, but has also been used by non-governmental organizations and businesses. Front groups are a form of disinformation, as they mislead the public about their true objectives and who their controllers are. Most recently, disinformation has been deliberately spread through social media in the form of "fake news", disinformation masked as legitimate news articles and meant to mislead readers or viewers. Disinformation may include distribution of forged documents, manuscripts, and photographs, or spreading dangerous rumours and fabricated intelligence. Use of these tactics can lead to blowback, however, causing such unintended consequences such as defamation lawsuits or damage to the dis-informer's reputation.

Worldwide: 

Soviet disinformation: 

Russian disinformation: 

Chinese disinformation: 

American disinformation: The United States Intelligence Community appropriated use of the term disinformation in the 1950s from the Russian dezinformatsiya, and began to use similar strategies during the Cold War and in conflict with other nations. The New York Times reported in 2000 that during the CIA's effort to substitute Mohammed Reza Pahlavi for then-Prime Minister of Iran Mohammad Mossadegh, the CIA placed fictitious stories in the local newspaper. Reuters documented how, subsequent to the 1979 Soviet Union invasion of Afghanistan during the Soviet–Afghan War, the CIA put false articles in newspapers of Islamic-majority countries, inaccurately stating that Soviet embassies had "invasion day celebrations". Reuters noted a former U.S. intelligence officer said they would attempt to gain the confidence of reporters and use them as secret agents, to affect a nation's politics by way of their local media.
In October 1986, the term gained increased currency in the U.S. when it was revealed that two months previously, the Reagan Administration had engaged in a disinformation campaign against then-leader of Libya, Muammar Gaddafi. White House representative Larry Speakes said reports of a planned attack on Libya as first broken by The Wall Street Journal on August 25, 1986, were "authoritative", and other newspapers including The Washington Post then wrote articles saying this was factual. U.S. State Department representative Bernard Kalb resigned from his position in protest over the disinformation campaign, and said: "Faith in the word of America is the pulse beat of our democracy."
The executive branch of the Reagan administration kept watch on disinformation campaigns through three yearly publications by the Department of State: Active Measures: A Report on the Substance and Process of Anti-U.S. Disinformation and Propaganda Campaigns (1986); Report on Active Measures and Propaganda, 1986–87 (1987); and Report on Active Measures and Propaganda, 1987–88 (1989).
According to a report by Reuters, the United States ran a propaganda campaign to spread disinformation about the Sinovac Chinese COVID-19 vaccine, including using fake social media accounts to spread the disinformation that the Sinovac vaccine contained pork-derived ingredients and was therefore haram under Islamic law. Reuters said the ChinaAngVirus disinformation campaign was designed to "counter what it perceived as China’s growing influence in the Philippines" and was prompted by the "[fear] that China’s COVID diplomacy and propaganda could draw other Southeast Asian countries, such as Cambodia and Malaysia, closer to Beijing". The campaign was also described as "payback for Beijing's efforts to blame Washington for the pandemic". The campaign primarily targeted people in the Philippines and used a social media hashtag for "China is the virus" in Tagalog. The campaign ran from 2020 to mid-2021. The primary contractor for the U.S. military on the project was General Dynamics IT, which received $493 million for its role.

Response: 

Responses from cultural leaders: Pope Francis condemned disinformation in a 2016 interview, after being made the subject of a fake news website during the 2016 U.S. election cycle which falsely claimed that he supported Donald Trump. He said the worst thing the news media could do was spread disinformation. He said the act was a sin, comparing those who spread disinformation to individuals who engage in coprophilia.

Ethics in warfare: In a contribution to the 2014 book Military Ethics and Emerging Technologies, writers David Danks and Joseph H. Danks discuss the ethical implications in using disinformation as a tactic during information warfare. They note there has been a significant degree of philosophical debate over the issue as related to the ethics of war and use of the technique. The writers describe a position whereby the use of disinformation is occasionally allowed, but not in all situations. Typically the ethical test to consider is whether the disinformation was performed out of a motivation of good faith and acceptable according to the rules of war.