Quick Locking System, pretty much describes it...

Safariland QLS (Quick Locking System)

When you make an investment in a good holster, it’s nice to not have to re-accomplish that purchase.  The Safariland Quick Locking System (QLS) helps in this regard.  By attaching the Locking Fork to your Safariland Holster, and then attaching a Receiver Plate to your gear, you can effectively move your holster from one platform to another in a matter of seconds.  This is great when you need to scale your gear depending on your environment.

You can find the Safariland QLS Kit in Black or Flat Dark Earth as well as individual Receiver Plates.

In seconds you can move your pistol (in it’s holster) from one platform to another depending on requirements.