See Antenna Gain.
The Generic Attribute layer is a layer of the Bluetooth protocol stack which manages the data transmitted through the Attribute protocol. It is responsible for establishing operations and framework for attribute data, which is the primary type of data sent and received in Bluetooth Low Energy communication.
The GATT layer is also the layer through which Bluetooth Smart (single-mode) devices may enjoy mediated communication with each other. Typically, single-mode devices are only able to maintain one connection at a time, and usually to the device occupying the Central role. However, in a GATT connection with the Central device, the Smart devices may communicate to each other through the Central device by acting simultaneously as GATT clients and GATT servers.
Note: Settings may vary depending on your version of the SCU.
General Purpose Input/Output. A factory standard generic pin. By default it has no purpose, allowing for assignment later should a spare pin be needed. This saves on having to rearrange pins and insert a new one.
Graphical User Interface.