Vermeil is a sterling silver piece covered in a layer of gold.
The Federal Trade Commission (FTC) has established guidelines for placing the vermeil label on an object. The FTC requires that vermeil objects must contain at least 2.5 microns of gold that is a minimum of 10K (it can be more and still be called vermeil).
Vermeil vs. Gold Plating
Gold electroplating requires that the gold layer be at least 7 millionths of an inch making vermeil 14 times thicker than gold plating.