What term describes the unique identifier assigned to devices on a network?

The correct answer is the MAC address, which is a unique identifier assigned to network interfaces for communications on the physical network segment. Each device on a network has its own MAC address, which is used to distinguish it from other devices within the same local network. This address is embedded into the network interface card (NIC) of the device and is crucial for the data link layer operations in networking.

The MAC address operates at a lower level than an IP address, which is more about routing packets across networks. While domain names serve as human-readable addresses that correspond to IP addresses, they are not unique identifiers assigned to devices themselves. A subnet mask, on the other hand, is used in networking to define the range of IP addresses that belong to a particular subnet, but it does not identify individual devices. Therefore, the concept of a unique identifier directly points to the MAC address as the correct response.