Media Access Control Address
Media Access Control Addresses (usually shortened to the acronymic form, MAC Addresses) are the network addresses for network interfaces, on Ethernet and other LANs which use the Ethernet packet format (including its physical network addresses). They are 48 bits long, globally unique, and only uniquely identify network interfaces; they do not include any other operationally useful information, such as where, in the particular internetwork to which the given network interface is attached, it actually is.
MAC Addresses are assigned permanently to network interfaces at the time of manufacture, from a namespace in which each manufacturer is perpetually assigned a section of the namespace. That way, users do not have to assign addresses to network interfaces, before attaching them to a physical network, as they used to have to do in the early days of networking, when network interface addresses were often only 8 bits long, and were not globally unique.