So glad you asked.
This is apparently a word used to describe a lack of interest or enthusiasm for a thing or task.
Yes, folks - the English language has evolved yet again. We've moved from "whatever" to "meh." Not that I mind, it's certainly easier to say:
"We need to do laundry." "Meh."
"Bush is still in office." "Meh."
But it does speak of deeper meanings. The word "w00t!" made it in, and I happen to think that's a good thing. Made-up words are finding their way into the actual lexicon of English. Unlike the French, who decided some time ago that not only was creating new words beyond their capacity, but that using other people's words for them ("television," "sexy," etc.) was also bad.
The French don't "watch TV," they "look at the box with lights," or something like that, I guess. At least the Germans (not what one would think of as a country known for it's flexibility of thinking) came up with a cool name for TV: Fernsehen, or far-seeing.
And while we're willing to come up with new names for things we already had names for, we still don't adapt well to change, unless it's something everyone has either done, or seen on das Fernsehen.
Or in other words, meh...