What is a Mobile Boarding Pass (QR Barcode)?

It is the QR (square) code that can be used instead of the boarding pass. After online check-in, it will be sent to your mobile device via SMS or e-mail. 

• Passengers who check in online and do not have baggage can join the flight with a QR Barcode by going directly through the security lane without stopping at the check-in counter at the airport. Passengers with luggage must go to the online check-in counters at the airport and hand over their luggage.
• When checking in for transfer flights, we recommend that you get the boarding pass for each flight at the same time to save time. 

→  What is online check-in? Where and how is done?

→ Rules of Baggage on Air Travel