The rods, fitting brackets, rings and (optional) cording mechanism used to hang window curtains, bed curtains and, on occasion, Roman blinds. Poles are mostly made from wood and metal, though also in perspex, glass, zinc and brass.
A pole can be anything, so long as it fits the space and holds the curtains: there is nothing to stop you using anything remotely suitable, including tree branches, bamboo canes, broom handles, whittled sticks…