1. The concept that a person's perception and how they 'feel' about things supersedes fact

2. The complete disregard for any body of evidence or advice from the scientific community when contesting facts

3. Negation of events or information widely accepted to be true

From Yahoo! News:
Colbert: AP the Biggest Threat to America By JAKE COYLE, AP Entertainment Writer
54 minutes ago

Stung by a recent Associated Press article that didn't credit him for coining the word "truthiness," Comedy Central's Stephen Colbert has struck back.

The world's oldest news organization, Colbert says, is the "No. 1 threat facing America."

On Wednesday evening, Colbert placed the AP atop the Threat Down segment of "The Colbert Report" show. What was No. 2?

Bears.

In October, on Colbert's debut episode of the "Daily Show" spinoff, the comedian defined "truthiness" as truth that wouldn't stand to be held back by facts. The word caught on, and last week the American Dialect Society named "truthiness" the word of the year.

When an AP story about the designation sent coast to coast failed to mention Colbert, he began a tongue-in-cheek crusade, not unlike the kind his muse Bill O'Reilly might lead in all seriousness.

"It's a sin of omission, is what it is," Colbert told The AP on Thursday. "You're not giving people the whole story about truthiness."

"It's like Shakespeare still being alive and not asking him what `Hamlet' is about," he said.

The Oxford English Dictionary has a definition for "truthy" dating back to the 1800s. It's defined as "characterized by truth" and includes the derivation "truthiness."

Michael Adams, a visiting associate professor at North Carolina State University who specializes in lexicology, pointed to that definition and has said Colbert's claim to inventing the word is "untrue." (Adams served as the expert opinion in the initial AP story.)

"The fact that they looked it up in a book just shows that they don't get the idea of truthiness at all," Colbert said Thursday. "You don't look up truthiness in a book, you look it up in your gut."

Though slight, the difference of Colbert's definition and the OED's is essential. It's not your typical truth, but, as The New York Times wrote, "a summation of what (Colbert) sees as the guiding ethos of the loudest commentators on Fox News, MSNBC and CNN."

Colbert, who referred on his program to the AP omission as a "journalistic travesty," said Thursday that it was similar to the much-criticized weapons of mass destruction reporting leading up to the Iraq War.

"Except," he said, "people got hurt this time."

Stephen Colbert defines truthiness as "The quality by which one purports to know something emotionally or instinctively, without regard to evidence or intellectual examination".

According to an interview Stephen Colbert gave on 60 minutes, he defined it this way:

"Truthiness is what you want the facts to be, as opposed to what the facts are. What feels like the right answer, as opposed to what reality will support."

An opinion of what is true, unincumbered by the facts

derives from the word 'truth'; a satirical term to describe things that a person claims to know intuitively or "from the gut" without regard to evidence, logic, intellectual examination, or facts

truth by consensus

1.)Describes things that people claim to know,something like a gut feeling.
2.)Straightforward truthfulness.
3.)Being a badass and reinventing the word truthiness without even knowing.

The amount of truth a statement has.