What is /dev/cu.Bluetooth-Incoming-Port and /dev/cu.iPhone-WirelessiAP So I was flashing my ESP8266 using Arduino and when selecting  the port for flashing I saw this:



I don't know what the red highlighted ports mean? What are they? And what happens if I flash them?
They are virtual serial ports matching paired/connected Bluetooth devices. For example "iPhone-WireeiAP" refers to tethering your computer to your iPhone to use its internet connection from your Mac. This can be implemented via a virtual serial port served over Bluetooth - however, it is obviously not done from your Arduino flashing tool.

The menu just lists any serial port found on your system - it does not indicate that they can be flashed. For example you cannot flash your iPhone this way.

If you try and flash them anyways, most probably nothing will happen at all. You will risk that while flashing you're sending something that the remove device (could be anything really) interprets as a correct command. Then you could risk for example altering settings on the device, or any other type of facility offered through the virtual serial port. Most likely everything will just be rejected as invalid commands though.