Other forms: misinformations
Something that's stated as a fact but isn't true is misinformation, especially if this is done on purpose. During a political campaign, one candidate might accuse another of spreading misinformation about her.
Misinformation is sometimes simply incorrect, like when your friend explains the mechanics of how airplanes fly but gets most of the details wrong. There's also the kind of misinformation that's deliberate, meant to hurt someone's reputation or keep secrets hidden. A government might release misinformation to hide classified details from spies, for example. When you add the "bad or wrong" prefix mis- to information, you get misinformation.