A Media Access Control (MAC) address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. It is a hardware identifier that uniquely identifies each device on a network, and is often found on a devices network interface controller (NIC) card. MAC addresses are used in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth.

MAC addresses are used in the medium access control protocol sublayer of the data link layer in the Open Systems Interconnection (OSI) network model. They are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or without a separator. On broadcast networks, such as Ethernet, the MAC address is expected to uniquely identify each node on that segment and allows frames to be marked for specific hosts.

There are three types of MAC addresses: unicast, multicast, and broadcast. A unicast address is attached to a specific NIC on the local network, while a multicast address is used to send a message to a group of devices on the network. A broadcast address is used to send a message to all devices on the network.

MAC addresses and IP addresses are two different things that sit in different layers of the Open Systems Interconnection (OSI) model. While IP addresses are hierarchical and used for routing packets across the internet, MAC addresses are used for identifying devices on a local network.

It is important for MAC addresses to be unique within a LAN network, as having two or more devices with the same MAC address can cause the network to not work properly. MAC addresses are preconfigured by the manufacturers and cannot be assigned to a device's NIC.