A unique identifier for all physical computers.
They are binary numbers that are 48 bits long.
The first 24 bits represent the OUI
They are usually represented with 12 hexadecimal characters.
Concepts
2 Devices Same MAC Address
Since MAC addresses are intended to be globally unique, if 2 devices have the same MAC address due to MAC Address Spoofing, then traffic will be sent to both addresses. This causes ARP issues, however Cisco router’s can handle this and will often delist the 2nd MAC address device. Oftentimes, MAC addresses will be reused. For the most part, this does not cause issues as its very unlikely 2 of the same mac address devices are on at the exact same time, but for local area networks this may pose a problem if not using a Cisco router.