"Mu", the concept in Zen Buddhism (not to be confused with "mu" the Greek letter, or "Mu" the lost continent, or the Marvel Universe, or Manchester United) is basically as described in this strip: a null or "N/A" answer, an invitation to expand your mind outside of an implied either-or binary framing, a rejection of the question as invalid and unanswerable.
Or, at least, that's the concept as understood by white nonBuddhists who skimmed "Zen and the Art of Motorcycle Maintenance" at some point in high school. In reality, of course, any glib one-sentence explanation of a koan that boils it down to a relatively simple concept completely misses the point. Koans are supposed to break your brain a little bit, and I'm willing to bet that neither today's comic nor this comment so far have done so to you, fair reader.
Koans are sort of like movies with twist endings - if someone tells you how how they go and what they "really mean" right off the bat, then you haven't truly experienced them, nor have you gained their intended benefit. I, personally, like to interpret "mu" as "fuck off, kid".
Is ice cream tasty?
I guess if I wrote a book on the subject to be read by the next generation of high schoolers, I'd probably call it "Zen and the Art of Fucking Off". I think kids these days need to learn the value of fucking off.
Why do people let me write things?