Rakuten American Express Card: what is Rakuten Dining?

I received an USPS flyer about the credit card, then looked up its website https://www.rakuten.com/american-express-card

Is it good and popular credit card? I don't do a lot of online shopping, so it does not seem to fit me well.

What does Rakuten Dining mean? What is the difference between Rakuten Dining and regular restaurant transaction?