A reel of flux impregnated copper desoldering braid (a.k.a. solder wick) for soaking up solder and cleaning soldering points on a PCB.
To use: Place the solder wick over the area to be desoldered, apply your hot soldering iron and the solder will be soaked up into the braid, repeat with a fresh area of braid until the joint is free from excess solder.