What is the use of "Bridge With" option in LAN Interface configuration?

[Bassam]

Dear Folk,
I am trying to drill down pfsense and learn all the features that is supports in order to get 100% familiarity. However, there is a "Bridge With" option at Interfaces -> LAN configuration page. I just want to know what is the use of it, and how does it work. Unfortunately, this is not documented in PFSense documentation nor available in m0n0wall. So may I have any clarifications form you guys regarding it.

Your help is much appreciated

Regards
Bassam

[hoba]

Have a look at http://pfsense.trendchiller.com/transparent_firewall.pdf