MAC Filtering

In computer networking, MAC Filtering (or EUI filtering, or layer 2 address filtering) refers to a security access control methodology whereby the 48-bit address assigned to each network card is used to determine access to the network.
MAC addresses are uniquely assigned to each card, so using MAC filtering on a network permits and denies network access to specific devices through the use of blacklists and whitelists. While the restriction of network access through the use of lists is straightforward, an individual person is not identified by a MAC address, rather a device only, so an authorized person will need to have a whitelist entry for each device that he or she would use to access the network.
While giving a wireless network some additional protection, MAC filtering can be circumvented by scanning a valid MAC (via airodump-ng) and then spoofing one's own MAC into a validated one. This can be done in the Windows Registry or by using commandline tools on a Linux platform.

Thanks to:
http://en.wikipedia.org/wiki/MAC_filtering