Air Shodou is an art form related to calligraphy (the name comes from a Japanese word meaning calligraphy). You use a program called Microsoft Kinect, which has a sensor that can feel a person's movements in the area in which it is installed. You then use hand and body movements to control what is called the writing brush - it looks as if you are just 'drawing in the air' with your hand (or whateve movements you choose to make) and a trail appears, which looks a bit like the trail of smoke you see in a flying display from a plane. Your actions will be displayed on a screen, with you appearing just as a shape.
People who are skilled in this form use it to write messages and even to create artworks - you can see some examples here.
You can read a bit more about Air Shodou here.