What is RLV
From (CTS) Wardrobe Wiki
RLV stands for "Restrained Love Viewer" which is a viewer based on the Linden Labs viewer except that it has a added functionality that allows scripted objects to control objects you wear, how your viewer behaves, and how you can access a special folder in your inventory.
More commonly RLV refers to the set of added functionality that has been published and added to most other viewers with the exception of the Linden Labs viewer. To enable RLV in the Firestorm viewer see Enabling RLV in Firestorm
When someone refers to their "RLV Folder" they are referring to the special folder in the inventory that the scripted objects can access.
For more information regarding RLV, see Marine's Blog at [1].