QR stands for Quick Response. It's basically a quick, scannable barcode-like image that takes you to a specific digital destination. QR codes can be a great voting tool allowing students to vote by simply scanning the code as they enter or exit the classroom. This can save time, and it gets your students up and moving.
QR codes are a great arsenal for the teacher tool belt. This technology is a tool and needs to fit a purpose. It can help create engagement in a lesson, manage your classroom, be part of student work or facilitate inquiry in a project. See this video on ideas for using QR codes.