Connecting over with with mavlinkshell.py: What does "0.0.0.0" mean?

Hi there! I’ve been searching this on internet but didn’t manage to find an explanation.

I have a PIxracer board with a ESP 8266 module running mavesp8266 firmware.

I manage to access the NSH console using the script mavlinkshell.py under the “Tools” directory of the PX4 source code. For this, I run:

./Tools/mavlinkshell.py --baudrate 921600 0.0.0.0:14555

And it connects without any problem.

My question is: what exactly is “0.0.0.0”? Is it a flag for the script to try to find the correct ip adress by itself, or is it a real ip address? If it’s the first case, how can I find the correct IP that I use to access the Pixracer’s console?

Thanks in advance!