A square holding a short piece of text — usually a web address or a payment request. You cannot see where it leads until you open it.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a barcode that can hold a sentence.
For example
You point the camera at a square on a restaurant table and the menu appears. You had no idea where it was going until it opened.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.