A QR code is a two-dimensional graphic image that encodes data and is read by a camera; in cryptocurrencies it is used to quickly transmit addresses and payment details.
A merchant is a trade or service business that accepts payment cards and, in many cases, cryptocurrencies. The term comes from the English word merchant.
A merchant account is a special trade account for a business used to accept non-cash payments by cards and over the internet. It links the seller to the payment infrastructure and the acquiring bank.
A microtransaction is a payment of a very small amount, often less than the minimum monetary unit. Such operations are unprofitable for traditional payment systems because of fees, while cryptocurrencies make them feasible.
BitPay is a payment service that allows merchants to accept payments in Bitcoin and other cryptocurrencies, acting as an intermediary between buyer and seller.