Disinformation is false or misleading information deliberately spread to deceive people, or to secure economic or political gain and which may cause public harm. Disinformation is an orchestrated adversarial activity in which actors employ strategic deceptions and media manipulation tactics to advance political, military, or commercial goals. Disinformation is implemented through coordinated campaigns that "weaponize multiple rhetorical strategies and forms of knowing—including not only falsehoods but also truths, half-truths, and value judgements—to exploit and amplify culture wars and other identity-driven controversies."

In contrast, misinformation refers to inaccuracies that stem from inadvertent error. Misinformation can be used to create disinformation when known misinformation is purposefully and intentionally disseminated. "Fake news" has sometimes been categorized as a type of disinformation, but scholars have advised not using these two terms interchangeably or using "fake news" altogether in academic writing since politicians have weaponized it to describe any unfavorable news coverage or information.

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.

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'.