Zari (or Jari as traditionally called) is basically a tinsel thread meant for weaving and embroidery. It is manufactured by winding or wrapping (covering) a flattened metallic strip made from pure gold, silver or slitted metallised polyester film, on a core yarn, usually of pure silk, art silk, viscose, cotton, nylon, polyester, P.P., mono/multi filament, wire, etc.
http://en.wikipedia.org/wiki/Zari