MAC Address or Physical Address.

MAC is stands for Media Access Control. This is also called Physical Address or Hardware address. MAC works on layer 2 or Data link layer of OSI model. All devices on LAN must have a unique MAC address . A MAC address is a 48-bits address burned into a Network Interface Card (NIC). The first 24 bits of MAC address indicate the vendor that Manufactured the Network Interface Card (NIC). This is called the Organization Unique Identifier (OUI). The last 24 bits of the MAC Address are the unique host address. 

A MAC address is looka like the below given example.

 00-68-4a-e8-9d-da

in this example- Vendor ID --  00-68-4a

                            Host ID   --  e8-9d-da

MAC address is always in Hex a decimal format.

it use the No. 0 - 9

and use alphabets a - f

Any Computer LAN Card making Company get registration in IEEE. and IEEE provide a 24 bits ID to this company.