PAA: It’s a dismissive. Apparently there is debate whether the origin was a Simpsons episode or a random internet chat room about some TV series (don’t remember what). Either way, though, I like it.
From dictionary.com
meh [me]
interjection
1.
adjective
2.
unimpressive; boring: The first few songs were meh.
3.
bored or apathetic: I’m feeling a little meh.
Origin:
1990-95; popularized on the TV show The Simpsons