MAC

In computer networking, a Media Access Control address (MAC address), Ethernet Hardware Address (EHA), hardware address, adapter address or physical address is a quasi-unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number.

http://en.wikipedia.org/wiki/MAC_address

see also MacOsX, iMac, Apple Macintosh, MacBookPro, etc.