A MAC address (Media Access Control address) is a unique hardware address assigned to the network interface of a device. It is used for network communication at the data link layer of the OSI model. A: unique network address that identifies the network interface of a device - Incorrect. This describes an IP address. B. unique network interface address that is provided by the DHCP server - Incorrect. MAC addresses are hardware-based, not provided by DHCP. C. unique hardware address that identifies the network interface of a device - Correct. This is the correct definition of a MAC address. D. unique hardware interface address that is provided by the central switch - Incorrect. MAC addresses are not provided by switches. References: * Cisco MAC Address Basics