Right. Unpaid balance over at least one month. Although some people probably just have a credit card for emergency purposes, I assume that most people who have a credit card do use it over the course of a year.
There's a bit of HN bias here. Just thinking of the lower income or non-white side of the country. So many people don't even have a checking account (4.5% households or 5.9million )[0] let alone a debit card. There's no way they have credit cards.
While it may be a low percentage number, 5-7million people is not "nobody". Question I would stipulate would be adults vs minors in that number.