LSL Protocol/Restrained Love Relay/Introduction
Marine Kelley modified the Second Life viewer to disable functionality in order to make "restraints" more real (or less prone to cheating). This modified viewer got code-named "Restrained Life Viewer".
Many avatars in SecondLife when asking questions such as "do you use it?" use abbreviations such as RL (Restrained Life), RV (Restrained Viewer) or RLV (Restrained Life Viewer). These abbreviations also cover many other views supporting the patches/extensions that have been done.
By 2008 there are several to possibly many other viewers that one can use now with this support.
Restrained Life Relay
Additional support was added to enable objects such as cages, furniture and so on to also disable functionality. This support works by communicating the commands through a script associated with the avatar (controlled by the viewer). This indirection is frequently described as a "relay".
Discussions in SecondLife either talk about "relay" or use abbreviations such as "RLVR".
The documents associated with this portion of the wiki discuss the "relay" or Restrained Life Relay API.