(M-e-h), Is THE word when there are no words. It can be used to describe how you're feeling, what something's like, a sound effect, can be used as a decleration of frustration or if you just can't be bothered speaking when someone asks you stuff.
Person 1 - 'hey, how was your day'
Person 2 - 'Meh!'
Person 1 - 'i won £9000 on the lottery, but then lost it all playing backgammon'
Person 2 - 'Mmmmeh!'