A word used when one does not wish to talk, doesn't really care, or just can't think of a good answer.
It can mean a variety of things, like yes, no, maybe, i don't know, and hence why it is used so often now, as humanity gets lazier and lazier.
REAL MSN CONVERSATION- TAKEN FROM MY HISTORY
Friend- huh are you mad at me?
Friend- you seem mad
Me - meh...
-end of convo-