A Media Access Control (MAC) address is a unique address for networked devices, based on the hardware of the device.
You'll find the MAC address on the base of your Orcon NF4V/NF18 modem.
The last 6 digits of this MAC address are the password to login to your modem's interface (all lower-case).
For example, the password to log in to the modem would be "a57993".
For help logging into your modem settings, check out configuring your modem.