A MAC address may be the address of your Mac, but they’re not interchangeable. MAC stands for Media (or Medium) Access Control, a geeky term for a part of network communications between the actual hardware, like a Wi-Fi radio or ethernet chip and jack, and the data that flows over it. Every network adapter has a unique MAC address set by the manufacturer during production.
Why should you need to know a device’s MAC address? It can come in handy when you want to configure features on your router. You’re probably familiar with an IP (Internet Protocol) address, one that uniquely identifies your computer, phone, or other hardware’s connection on the internet. A MAC address applies only to the local area network—the collection of devices connected physically together or via Wi-Fi.
Because you almost always rely on a network router to assign IP addresses to your devices, the router can’t use an IP address to identify your hardware first. That’s where the MAC address comes in.
Read more at Macworld.com