Truthiness is the quality of stating concepts one wishes or believes to be true, rather than the facts.
Origin: Stephen Colbert, "The Colbert Report," 2005
"And that brings us to tonight's word: truthiness.
"Now I'm sure some of the Word Police, the wordanistas over at Webster's, are gonna say, 'Hey, that's not a word.' Well, anybody who knows me knows that I'm no fan of dictionaries or reference books. They're elitist. Constantly telling us what is or isn't true, or what did or didn't happen. Who's Britannica to tell me the Panama Canal was finished in 1914? If I wanna say it happened in 1941, that's my right. I don't trust books. They're all fact, no heart."
Truthiness is the characteristic of an assertion or argument that “feels right,” especially one that is made authoritatively, without considering the evidence or engaging with opposing views.
...The concept was introduced in the October 17, 2005, premiere episode of Stephen Colbert's Colbert Report, a satirical news show...It became Merriam-Webster's Dictionary's Word of the Year the following year, and appears in the Oxford English Dictionary. The concept resonated as much as it did because it attaches a vivid descriptive name to an important phenomenon in rhetoric and leadership: the appeal to emotion, especially one framed in a way to cast aspersions on recourse to conflicting facts."
--Leadership Glossary: Essential Terms for the 21st Century, Credo Reference.
"The compound word post-truth exemplifies an expansion in the meaning of the prefix post- that has become increasingly prominent in recent years. Rather than simply referring to the time after a specified situation or event – as in post-war or post-match – the prefix in post-truth has a meaning more like ‘belonging to a time in which the specified concept has become unimportant or irrelevant’. This nuance seems to have originated in the mid-20th century, in formations such as post-national (1945) and post-racial (1971).
Post-truth seems to have been first used in this meaning in a 1992 essay by the late Serbian-American playwright Steve Tesich in The Nation magazine. Reflecting on the Iran-Contra scandal and the Persian Gulf War, Tesich lamented that ‘we, as a free people, have freely decided that we want to live in some post-truth world’. There is evidence of the phrase ‘post-truth’ being used before Tesich’s article, but apparently with the transparent meaning ‘after the truth was known’, and not with the new implication that truth itself has become irrelevant.
A book, The Post-truth Era, by Ralph Keyes appeared in 2004, and in 2005 American comedian Stephen Colbert popularized an informal word relating to the same concept: truthiness, defined by Oxford Dictionaries as ‘the quality of seeming or being felt to be true, even if not necessarily true’. Post-truth extends that notion from an isolated quality of particular assertions to a general characteristic of our age."
Image and text from Oxford Dictionaries https://en.oxforddictionaries.com/word-of-the-year/word-of-the-year-2016