You may have seen rectangles with lots of dots – like this one:
These are called QR codes and are a way to code information so that a phone camera can easily interpret it. The one above has my contact details in a Vcard format and anyone who scans it will add my details to their contact list.
This may not sound like too much use to you, but many sorts of information can be encoded. For example, details of an event that you are asking people to in one code and location details in another. Then you can put them into your email, letter or advertisement so that people can add it to calendars with no fear of errors, (as long as you get it right!)