Wikipedia: MAC address

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A 'Media Access Control address' or MAC address is a 48-bit identifier used to assign addresses in OSI Layer 2 networks. MAC addresses are assigned by the IEEE, and are used in the following network technologies:

A 'Media Access Control address' or MAC address is a 48-bit identifier used to assign addresses in some OSI Layer 2 networks. MAC addresses are assigned by the IEEE, and are used in the following network technologies:

Changed: 12c12

They are also closely related to NSAP addresses.

See also: NSAP address for another endpoint addressing scheme.

Ethernet
Token Ring
802.11? wireless networks
ATM (switched virtual connections only, as part of an NSAP address)

: add more technologies here...

Since the original designers of Ethernet had the foresight to use a 48 bit address space, there are potentially 2⁴⁸ or 281 million million possible MAC addresses. The IEEE hands out 24-bit OUI prefixes to organizations, effectively allocating blocks of 2²⁴ (around 16 million) MAC addresses at a time.

See also: NSAP address for another endpoint addressing scheme.

External links:

http://standards.ieee.org/regauth/oui/index.shtml