MAC stands for Media Access Control. This is the low level network connection. Every Media Access Control has a MAC Address that allows it to be identified. This address is globally unique and is assigned by the IEEE.
Each Media Access Control has one MAC Address but can have multiple IP Addresses.
The MAC Address is a 48-bit number and by convention is written as six hexadecimal numbers separated by colons, e.g.
A trailing subscript is sometimes added to clarify the number base:
The bit organisation of the MAC Address is shown in the diagram below:
The OUI or Organisationally Unique Identifier is assigned by the IEEE to each manufacturer of network equipment. The Product Identifier is then assigned by the manufacturer in such a way as to guarantee all its products have a unique number.
MAC Addresses have, for historical reasons, a number of alternative names including Ethernet Address, Hardware Address, Physical Address and Layer 2 Address.