On the back of your BT Business Hub 3 you have four yellow Ethernet ports that allow you to connect devices to the Hub. Port 4 is labelled as GigE.
GigE or Gigabit Ethernet is the way we talk about the technology for transmitting data at a rate of a gigabit per second (or 1,000 megabits per second). That's ten times faster than the other three ports, which transmit data at 100 megabits per second.
If you've got BT Business fibre, such as Infinity or Superfast, this allows devices that are connected to the GigE port to receive data at the same speed as it is received from the fibre connection.
If you've got BT Business Broadband then you can use the GigE port to connect big, fast hard drives known as Network Attached Storage devices.