Media Access Control Address

Aka MAC address, Ethernet IEEE 802 address, or link-layer address.

 0          1          2          3           4        
+--------+--------+--------+--------+--------+--------+
|      bb      OUI         |           NIC            |
+--------+--------+--------+--------+--------+--------+

OUI - Organizationally Unique ID   
NIC - Network Interface Controller
bit 6 (next to the last bit of the first octet) - Universial/Local (U/L) bit, "0" for global address, "1" for local address.
bit 7 (the last bit of the first octec) - "0" for unicast, "1" for multicast.