BLE stands for Bluetooth Low Energy. This shield is designed to work with Arduino boards or compatibles, including Arduino Uno, Mega 2560, Leonardo and Due. It allows you to connect your Arduino boards with other BLE Central device like a smartphone or tablet. So you can develop some applications like:
Control your Arduino pins with our/your own mobile App. Send sensor data from your Arduino to an App for processing. Use your mobile device as an internet gateway for your Arduino and much more! BLE shield could operate under 3.3V or 5V, therefore it works with a lot of Arduino compatible boards too.