There are three major categories or types of gold that can be designated, as follows:

Gold Filled (GF)
Gold-filled, also called gold overlay, refers to a layer of 10-karat or better gold that is permanently bonded by heat and pressure to a base metal, then rolled or drawn to a prescribed thickness. The gold content must be at least 10% of the total weight.

Rolled Gold Plate (RGP)
Rolled gold plate, also called gold overlay, is similar to gold-filled, except the gold layer is thinner. The gold content must be at least 10% of the total weight.

Gold Electroplated (GEP)
Gold-electroplated, or simply gold-plated, is defined as a layer of 10-karat gold or better plating that is bonded to a base metal. The gold content can be less than 5% of the total weight, but it must be properly identified by weight in terms of total metal content.

Gold Leaf
Gold leaf is very thin gold plating that is pounded and then applied by hand.

Vermeil
Vermeil is sterling silver covered with 120-millionths of an inch or more gold that has been electroplated or mechanally bonded to the silver.