Desoldering braid, also known as desoldering wick or solder wick, is finely braided 18 to 42 AWG copper wire coated with rosin flux, usually supplied on a roll.The end of a length of braid is placed over the soldered connections of a component being removed. The connections are heated with a soldering iron until the solder melts and is wicked into the braid by capillary action. 

The braid is removed while the solder is still molten, its used section cut off and discarded when cool. Short lengths of cut braid will prevent heat being carried away by the braid instead of heating the joint.