MAC address
Networking
A network card's 48-bit identifier, which ip link show prints after link/ether. It is local and disposable: as a packet crosses several routers the destination MAC is rewritten at every hop to name the next device, while the destination IP address stays unchanged from start to finish. A switch forwards on it and never reads an IP address; a router reads the IP and builds a fresh frame. Remembering which of the two changes at each hop settles half of all layer-2 confusion.
Also written: link/ether, hardware address