What exactly is the "Ochi-Sabi" often heard in Hello! Project?

When watching Hello! Project, you often come across the term "Ochi-Sabi".In fan reviews of concerts, you see things like "The ...

The first internal Hello! Project fan meetup was a blast

There are Hello! Project fans in every company, aren't there? At LY Corporation, there has long been an internal Slack ...
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Hello! Project 2003 Summer ~Yossha! Bikkuri Summer!!~ Where to Watch

Hello! Project 2003 Summer ~Yossha! Bikkuri Summer!!~ isn't available to stream, rent, or buy in your region right now. Check back soon or try a different region using the flag selector below. Not yet ...