Media Access Control Address

The MAC address, Media Access Control address, is a 12-digit, hexadecimal number which is burned into network interface card (NIC).  This address uniquely identifies a specific card and it is ultimately used for all communications to and from the device.   Although other people and even computer communication protocols will refer to a computer by different names or techniques, ultimately these other means are always reduced to the MAC address.  The MAC address can be thought of as analogous to the standard postal address of a home or business:  without a correct address, no mail can be delivered to the location.

As the name implies, the address is used to access the network media to which it is attached.  MAC addresses are ISO network model layer-2 constructs and can only be used to communicate to other MAC addresses on the same network domain or "piece of common wire".  Devices called routers act as gateways to other networks and provide an interface, thus a MAC address, on the "same wire", for each network attached to the router.