Final answer:
A 48-bit-long physical address called a Media Access Control (MAC) address uniquely identifies a network device and is used for communication on local networks.
Step-by-step explanation:
The 48-bit-long physical address used to identify a network device is known as a Media Access Control (MAC) address. Each network interface card (NIC) or device that connects to a network has a unique MAC address assigned by the manufacturer, which acts as a permanent identifier for that device on a local network segment. MAC addresses are used in a variety of network technologies including Ethernet and Wi-Fi to ensure devices can be correctly identified and communicated with.