What is NAT Punchthrough - Android

I am currently developing a game for android that has networking , But i am new to this so i don’t know what is NAT Punchthrough usefull for.
Oh and one more question , If i created the game for android can the user host a game with his external ip adress and others could join him ? So far i have tried it in lan only and he phone connected to the pc.
Thanks.

NAT

NAT punchthrough

If you’re connected via NAT-router, you need NAT punchthrough in order to be reachable from the internet. Note: not all router support this “hack”, so it’s never a guarantee you are reachable.