Common
Ordinary, Mediocre
noun, な adjective
You're so mediocre that you're flat. That's really common. Look at most of the midwest. It's really mediocre and flat too. And there's a whole lot of it out there.
へいぼん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
平凡な毎日に退屈していたんです。
I’m bored with the ordinary every day.