From Glossary of Theater & Stage Rigging Terms :
See the thread https://www.controlbooth.com/threads/extra-rope-on-fly-rail.20463/ for discussion.
A short piece of rope used to tie down a hand line [aka purchase line] to prevent movement.
See the thread https://www.controlbooth.com/threads/extra-rope-on-fly-rail.20463/ for discussion.