Copper foil is an adhesive backed copper ribbon mainly used for stained glass projects. It can also be used for decorative edging and can even be used for electronics! You use it by wrapping around the edges of glass and soldering together. It is known as copper foil technique or Tiffany Technique after its American inventor.
You can also use it to join many other materials.
3M Venturetape and EDCO copper foil tapes come in 33m rolls. ARCHS copper foil comes in 50m rolls which represents great value