A universal, non-commital answer to every question ever posed. Its the answer that deosn't actually give any answer.
"So, you wanna do something tonight?" "Meh"
"Done anything good this week?" "Meh"
"How was it?" "Meh"
'Meh' is also used in The Simpsons, Episode: Hungry, Hungry Homer:
[Homer]: Kids, how would you like to go... to Blockoland!
[Bart & Lisa]: Meh.
[Homer]: But the TV. gave the impression that--
[Bart]: We said "meh".
[Lisa]: M-E-H. Meh.