WHAT IS 'GOLD-FILLED'?
It is a layer of 10Kt or better gold mechanically bonded under heat & pressure to one or more surfaces of supporting base metal, then rolled or drawn to a given thickness.

The finished product has a surface layer of gold of the appropriate karatage, which is very thick compared to rolled gold plate or the heaviest electroplate (gold plated) material.
Gold-Filled items are generally considered life-time products, and the gold layer will not quickly wear off, as it will in electroplated products.