As Webster kindly points out, non-sequitur translates to "that which does not follow". As is was pointed out at the bottom of this node, "FISH FRY" is a kind of non-sequitur, as it does not logically follow from the rest of the node content.
In terms of logic, it is defined as an argument whose conclusion does not logically follow from its premises (Wikipedia). In other words, given that (eg.) a) all computers with the Intarnut have access to E2, and b) you have access to E2, it is a non-sequitur to say that you own a computer with the Intarnut. It may or may not be true (i.e. I could have a computer or a mobile phone), but it does not follow from the argument.
This form of non sequitur is called affirming the consequent, as opposed to denying the antecedent. An example of such is as follows: if a) you are in London, you are in England; and b) you are not in London, then you are not in England.
A different type of non sequitur is used in humour. Often a random word cried out can constitute a non sequitur. It may sometimes even be a sentence that is detached and unrelated from the rest of the speech, as is the case of a speech made by Rowan Atkinson in Not The Nine O'Clock News:
(as a judge in a courtroom) This case has been one of the most difficult and embarrassing of my whole career. You are an evil and malicious young trollop who has wilfully committed an evil crime, and yet you have come to this court, and without any consideration forced this unfortunate young man to behave like a cross between a human vegetable and Ronnie Barker! (Griff Rhys-Jones had earlier been mispronouncing legal words) You are someone who wantonly thrusts herself upon men for sexual fantasy wherever you may find them. Perhaps you'd like to join me for lunch?
If one is careful, once can combine the two types of non-sequitur: if all people dream when they sleep, and I am asleep, then my trousers are purple.
IMHO one does not appreciate humour until one appreciates irony, anticlimaxes and the non-sequitur. Carry on.