The MAC Address is an unique 12 characters address. It is the unique identifier of your network device. You can get the MAC address of your Mac OS X 10.7, or 10.8 (Lion or Mountain Lion) by following these steps.
1. Click on the Apple menu from the top menu bar.
2. Select Network from the drop down list
3. Choose your current active network connection (Wi-fi, Ethernet, etc.) from the left menu, then click Advanced button from the bottom right corner. You can find the Wi-Fi address, the MAC address of your Mac OS X 10.7, or 10.8 (Lion or Mountain Lion), see below figure.
Note that if you are on an earlier Mac OS X version, like OS X 10.6 Snow Leopard, the Wi-Fi address is called Airport Address. See Find Mac Address on OS X Snow Leopard or Leopard here.