Bitcoin Berlin in El Salvador is the perfect example.

Started with one business accepting Bitcoin and calling a local Bitcoiner every week to sell it for cash.

Until other businesses wanted to accept Bitcoin like the grocery store for example.

Then the businesses never called for cash anymore, they simply spent the sats.

Now there are 100 businesses or so accepting Bitcoin, you can literally get any product or service and pay in Bitcoin.

They use Blink so it's custodial but still an incredible circular economy.

So in short, a circular economy is when people accept bitcoin as payment and use that bitcoin to pay for other things.