A QR code is (according to Wikipedia) "a type of matrix barcode (or two–dimensional barcode) invented in 1994 by the Japanese automotive company Denso Wave. A barcode is a machine–readable optical label that contains information about the item to which it is attached."
Basically, it's one of those black–and–white squares that you point your phone at to be directed to a web page.
© Haydn Thompson 2021