Also called: Leap in logic
Non Sequitur is a Latin term literally meaning "it does not follow," and is commonly seen in discussions of logic; it's a whole class of fallacies including Affirmation of the Consequent, Denial of the Antecedent, Undistributed Middle and several others. Broadly, it applies to any argument where the conclusion does not flow naturally from the premises. Non Sequiturs are an important element in humour, but they're still fallacies when used as part of a logical argument.
Often, a non sequitur results from the writer believing that the statement results from an "obvious" argument that doesn't need to be explicitly stated.
For when this actually works as an argument, see Chewbacca Defense. When this is to such an extreme that attempts to consider it in any rational manner results in maddening frustration, it is Insane Troll Logic.