A QR code is a type of barcode which appears as a grid of black and white squares. These codes are often used to encode web URLs (such as the URL of a Fish Trax™ Marketplace Trace Code) that you can scan and access using a smartphone. You can learn more about QR codes here.
To scan a QR code, you will need a smartphone with a camera and an appropriate scanner app. There are many free scanner apps available for both Android and iOS devices. Some options include: