Samsung Gear VR is a mobile virtual reality device developed by Samsung Electronics in collaboration with Oculus VR. A compatible Samsung Galaxy device (Galaxy Note 5 or Galaxy S6/S6 Edge), sold separately, acts as the headset's display and processor, while the Gear VR unit itself contains the high field of view lenses as well as a custom IMU for rotational tracking which connects to the smartphone via micro-USB.
The Gear VR headset also includes a touchpad and back button on the side, as well as a proximity sensor to detect when the headset is on. The touchpad and button allow for a standard minimum input capability for users to interact with the virtual environments, whereas Google Cardboard devices only feature a button.
Source: Wikipedia, "Samsung Gear VR", available under the CC-BY-SA License.