What do hair pins have to do with networking? | Cookbook

Cookbook | FortiGate / FortiOS 5.4.0 | Fortinet Documentation Library

Using Hairpinning in a Network

What do hair pins have to do with networking?

Hair-pinning, in a networking context, is the method where a packet travels to an interface, goes out towards the Internet but instead of continuing on, makes a “hair pin turn”, and comes back in on the same interface. Initially, it may seem unnecessary or pointless even but it does serve a purpose.

https://docs.fortinet.com/document/fortigate/5.4.0/cookbook/105831/using-hairpinning-in-a-network