It's an adapter which allows you to send data from CSI camera over HDMI cable for up to 10m!

It's a perfect solution if you need to have your camera in different place than Raspberry Pi. For example using this adapter you can have camera outdoors while keeping your expensive RPI indoors. Additionaly you can connect sensors to this board using I2C or some other sensors using 3 left pins, for example a PIR or temperature sensor. This adapter is exact same size as Raspberry Pi Camera and has same hole size.