At its most basic level, an alternative fact is a statement that is presented as true, but is actually false or misleading. It is essentially a form of propaganda or disinformation that is designed to manipulate public opinion or shape public perception in a way that is favorable to the person or group presenting the alternative facts.

An alternative is one of the choices in a set of given options; typically the options are opposites of each other. So to talk about alternative facts is to talk about the opposite of reality (which is delusion), or the opposite of truth (which is untruth).