Ordinary, Mediocre
Noun and な adjective
へいぼん
平凡な毎日に退屈していたんです。
I’m bored with the ordinary every day.
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.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.