Thunderbolt bridge

The Thunderbolt Bridge will only be active when you have a connected device that requires it. The "bridge" is just a connection between Thunderbolt and another device or protocol. You will see the Thunderbolt Bridge as active if you connect an Ethernet cable to the Thunderbolt port as it bridges the Thunderbolt protocol to the Ethernet protocol. I believe I've only seen a Thunderbolt Bridge in relation to networking. Here is an article that may help:

https://arstechnica.com/gadgets/2013/10/os-x-10-9-brings-fast-but-choppy-thunderbolt-networking/

ThunderBolt Bridge is a software-only Device you can add to your list of Network devices. Its Driver supports ThunderBolt cable-to-ThunderBolt-cable connection which otherwise would just sit there and do nothing. That cable-to-cable connection is a little unusual, so Apple decided to use a separate Driver for that specific connection.

I don't think that ThunderBolt Bridge Driver is used for anything else. If you add a ThunderBolt-to-Ethernet adapter, you also must add a similar-sounding driver to the list of devices, before it can be configured. Its name sounds similar, but I don't think they have much in common..