What is a MAC address?
A media access control address (MAC address) is an unique identifier assigned to a network interface of any device (i.e. computers, mobile phones, routers...) with a network card. All wired (ethernet) and wireless IEEE 802 network interfaces need to have an unique MAC address, for to be able to communicate at the data link layer of a network segment. In a MAC address there are encoded specific vendor information such as the registered company identification number.
What is the vendor MAC address?
Every vendor encodes it's identification number into their MAC addresses of their devices. Therefore it is possible to detect the vendor of a specific network card, based on the MAC address of the network interface.