What Is A MAC Address?

[flopnite]

A MAC address is a unique identification number or code used to identify individual devices on the network. Therefore, it’s also sometimes referred to as a hardware or physical address.

These numbers are embedded into the hardware of the network device during the manufacturing process. While they usually remain constant, you can sometimes find and modify the MAC address settings through software.

MAC addresses are 12-digit hexadecimal numbers (48 bits or 6 bytes in length) and often written in MM:MM:SS:SS:SS format. They help with communication on the network, and also provide some ISPs with a secure means to authenticate devices or computers for internet access.

Source: MAC Address vs IP Address

[Ciscopro2000]

IP address is something a user or administrator assigns.  A MAC address is something a hardware manufacturer assigns and is unchangeable by the user. 

[Artemis3]

IP address is something a user or administrator assigns.  A MAC address is something a hardware manufacturer assigns and is unchangeable by the user. 

But is quite easy to spoof by the OS, and seems to be the late fashion.
Also some hardware lets you change it in their firmware, or needs to set it at boot time from an external file (driver).

To answer the OP question: It is a 48 bit address that is supposed to be unique for each network device.

[Vod]

To answer the OP question: It is a 48 bit address that is supposed to be unique for each network device.

But due to all the unregistered producers out there, only the right (least significant) part of the address should be considered unique in your network.

Also interesting, Apple is moving to a new advertiser id, that is based on hardware but changes monthly. 

[DTalerDev]

lol i thought you talk about some macintosh ^^
haha,    uhhmm its getting late here,
wish you all an nice evening