A Media Access Control address (MAC address) is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sublayer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address.
A host cannot determine from the MAC address of another host whether that host is on the same OSI Layer 2 network segment as the sending host, or on a network segment bridged to that network segment.
Now to find out your unique physical address either you can follow the command prompt method or you can straight find out the physical address from your ISP's support panel.
Click the Start button, select Run.
Then, Type CMD and click OK.
A black Command prompt window will open. Type ipconfig /all and press Enter. (Note the space between ipconfig and /all.)
Lots of information will be displayed, but what you need is in the Ethernet Adapter Local Area Connection section. Write down the Physical Address that looks like "0A-B2-C8-D3-E4-D9". This is the "MAC Address."
Your MAC Address (Physical Address) almost always starts with a zero. If you're writing down a number that does not start with "0" you've probably got the wrong number.
MAC address is unique identity of your computer. So, it is very important to know that address.