What is the significance of MAC address?

The MAC (Media Access Control) address is the physical address, which is assigned to the hardware network card (Network Interface Card), of the host computer and remains fixed. The machine on which the NIC is attached, can be physically identified on the network using its MAC address. The NIC manufacturer assigns a MAC address which is a 6 byte address (48 bits) with each byte separated by a colon. The first three bytes (24 bits) of MAC address are the manufacturer-id or the organizational unique identifier (OUI) and the last three bytes (24 bits) are the card-number.