A very general name for a metal (almost always an aluminum alloy, usually tubing) fabricated in such a way that it can be rigged and therefore support equipment that is to be used off the ground
. Most commonly truss is used to support lights and required paraphernalia, but also commonly known to support curtains and other set pieces to support (a most often temporary) set.
Specialty truss: folding, Swing
All photos from TomcatUSA