A two-dimensional barcode format that efficiently stores alphanumeric characters; often a URL. QR codes are often used for consumer applications as they are more recognizable as being a consumer barcode than other formats.
Data Matrix has started to replace QR Codes in several major deployments as Data Matrix is not encumbered by patent issues.
QR Codes have an error correction mechanism to handle unreadable parts of the image due to damage or dirt. There are four error correction levels available with different levels of correction. As the level of error correction increases, the data size of the barcode increases, which requires it to be printed larger to maintain readability.