Every Network interface device that use TCP/IP protocol (NIC or WNIC) will have a MAC address (Media Access Control address) on it.
By knowing the MAC address of a computer, tablet computer, smartphones, etc, you can set the access such as whether the device is allowed or not to access your network (eg wifi).
To know MAC address on the Android device :
(In the following example, I use Android 4.3 Jelly Bean)
1. Go to Settings menu
3. Tap on menu
4. Tap Advanced