A QR code (Quick Response code) is a two-dimensional barcode that stores data as a grid of black and white squares. Unlike a standard barcode, which encodes data in one direction only, a QR code encodes data in both directions — giving it far more capacity. Scan one with a phone camera and the encoded text is read instantly, with no app required on most modern devices.
What gets stored inside
A QR code stores raw text — nothing more. That text is usually a URL, but it can also be a phone number, a Wi-Fi credential, a contact card, or plain prose. The phone interprets the text after reading it; the code itself has no idea what happens with the result. There is no database lookup, no server call, and no connection made at the moment of scanning.
The anatomy of the pattern
Three square markers sit in the corners of every QR code. These are finder patterns — they let the camera determine the code's orientation and size instantly, even at an angle or in low light. The remaining cells store the encoded data plus redundant error-correction bits that allow a partially obscured code to still scan correctly.
How much data it holds
A QR code can hold several thousand characters depending on the data type, though in practice the shorter the payload, the less dense the pattern and the faster it scans. URLs are typically short enough that a QR code printed at business-card size scans reliably from a meter away.