Radioactive waste or radioactive residue was a type of hazardous material created as a volatile byproduct of a nuclear reaction.
In 2268, James T. Kirk suggested Montgomery Scott flush radioactive waste into the ventilation system in an effort to neutralize the dikironium cloud creature. (TOS: "Obsession")
The Orion vessel encountered by the USS Enterprise left trails of radioactive waste in its wake. (TAS: "The Pirates of Orion")