MAC address
A device's hardware address on the local network, six bytes like 24:6f:28:aa:bb:cc.
A MAC address is the 48-bit link-layer address of a network interface, used to deliver frames on one local network; it never leaves that network.
Examples
The greenhouse ESP32's MAC address is 24:6f:28:aa:bb:cc; the first three bytes, 24:6f:28, are the vendor prefix.
A MAC address is replaced at every router, so the distant server at 203.0.113.50 never sees the sensor's 24:6f:28:aa:bb:cc.
See also