What is a MAC address?
A Media Access Control (MAC) address is a 48-bit address that is used for communication between two hosts in an Ethernet environment (e.g. your local network or an office LAN). It is a hardware address, which means that it is stored in the firmware of the network interface card.
A MAC address is supposed to be globaly unique. Each network card vendor gets its share of addresses (represented by the first 24 bits) and assigns a unique MAC address to each card.
A MAC address is written in the form of 12 hexadecimal digits. For example, consider the following MAC address:
The first 6 hexacedimal numbers represent the manufacturer (HP in this example). The last six numbers are unique for each network card.