Hole punching is the process of taking advantage of the standard way of implementing NAT to allow direct connection between computers in private networks.
The process starts as normal proxy - two devices connect to the same public server:
The data flows through public server. The green circles represent the socket connections between devices, the blue line is the flow of data.
Now what it the server sends socket A to device B and vice versa?
Suddenly, both devices have each other's "address" and can send any information to each other:
