A QR code (Quick Response code) is a type of matrix barcode (or two-dimensional barcode) first designed in 1994 for the automotive industry in Japan. A barcode is a machine-readable optical label that contains information about the item to which it is attached. In practice, QR codes often contain data for a locator, identifier, or tracker that points to a website or application. A QR code uses four standardized encoding modes (numeric, alphanumeric, byte/binary, and kanji) to efficiently store data; extensions may also be used. QR codes are commonly used in marketing and advertising to direct users to websites, promotions, or contact information. They can also be used for authentication, payment processing, and data storage. The 'qrcode' file extension typically represents an image file (like PNG, JPEG, or SVG) that visually displays the QR code. The actual data encoded within the QR code is not directly stored in the file extension itself, but rather within the image's pixel arrangement.