A QrReader app is a simple application that allows users to scan QR codes using the camera on their mobile device. This app is typically used in conjunction with other apps, such as the MetroBooking app mentioned, where users can purchase tickets and receive a QR code for entry.
When a user scans the QR code using the QrReader app, it quickly processes the information contained within the code and verifies its authenticity. This ensures that the user has a valid ticket or pass for the intended purpose, such as boarding a train or entering an event.