The waste that is remained after the use of nuclear chemicals in the reactors. They are assemblies of metal rods, ceramic pellets, which are similar to the fuel loaded initially. They reacquire special techniques for their management and disposal.
Nuclear waste is the material that nuclear fuel becomes after it is used in a reactor. It looks exactly like the fuel that was loaded into the reactor assemblies of metal rods enclosing stacked-up ceramic pellets. But since nuclear reactions have occurred, the contents are't quite the same.