Tough Rubber Sheath (TRS) cable normally consists of a black outer sheath of rubber with several conductors.
In the United States this is obsolete wiring, formerly used circa 1949-1969. TRS is in current use in the United Kingdom where greater mechanical toughness is required than PVC provides.
When it was introduced, TRS cable largely superseded lead-sheathed cables and plain conduit wiring, except where mechanical damage was a hazard.