“Desoldering wick”! This is a very useful tool to desolder circuit when you make a mistake, or hacking toy circuits. I use them often but I never knew the name.. Here is the wikipedia explanation

“A solder wick, also known as a desoldering wick or desoldering braid, is a roll of fine, braided 18 to 42 AWG wire typically made from oxygen free copper that has been treated with a rosin solder flux.
The processes of removing solder with a wick start by placing the wick over the solder joint to be removed and then heating the portion of the wick in contact with the joint with a soldering iron. As the rosin melts onto the wick and the connection and the solder reaches its melting point the solder is sucked into the solder wick via capillary action. Heat is then removed and the solder is allowed to solidify before the wick is removed from the workpiece. Finally, the used section of wick is discarded.”