Short answers, pulled from the story.
A credit card lets the holder carry a continuing balance of debt subject to interest, while a charge card requires the balance to be repaid in full each month or at the end of each statement cycle. A credit card also involves a third-party entity that pays the seller and is reimbursed by the buyer, whereas a charge card simply defers the buyer's payment to a later date.
Bank of America launched the BankAmericard in Fresno, California in 1958, the first successful program recognizable as a modern credit card. It chose Fresno because 45% of residents banked there and mailed cards to 60,000 residents at once, and the licensees later united under the brand Visa in 1976.
In 2020 there were 1.09 billion credit cards in circulation in the United States, and 72.5% of adults, about 187.3 million people, had at least one credit card. Worldwide the count reached 7.753 billion cards.
Most financial institutions take the annual percentage rate, multiply it by the average daily balance, divide by 365, and multiply by the number of days the amount revolved before payment. If even $1.00 of a balance remains unpaid, interest is charged on the full amount from the date of purchase until payment is received.
Merchants pay interchange and discount fees, commonly around 0.5 to 4 percent per transaction, and because card contracts often barred passing the cost directly to card users, merchants raised prices for all customers. In 2008 credit card companies collected $48 billion in interchange fees in the U.S., an average of $427 per family, and rewards programs transfer about $1,282 from the average cash payer to the average card payer per year.
A secured credit card is secured by a deposit account owned by the cardholder, who typically must deposit between 100% and 200% of the credit desired, though incentives can lower it to as little as 10%. It helps people with poor or no credit history build credit because most issuers report regularly to the major credit bureaus.
Unsolicited mass mailings of credit cards, known in banking as drops, were outlawed in 1970 due to the financial chaos they caused. By the time the law took effect, approximately 100 million credit cards had already been dropped into the U.S. population, after which only applications could be sent unsolicited.