The term 1/20 or 1/10 10K, 12K, 14K has to deal with the government regulation of the amount of gold that must be in a piece of jewelry. I have copied and pasted the definition from ebay guides below. I hope that this answers your question. If not just google gold filled and their will be numerous hits explaining the what gold filled actually means.
Gold filled items are regulated by the government. These items are therefore so much better then gold plated which has no regulations at all. Gold filled jewelry is made from solid gold and filled with other alloys such as rhodium (a member of the platinum family), brass, and sterling silver. Gold filled wears, looks and lasts like solid gold because its outer surface IS solid gold. Everything you can see and touch is pure gold. In the jewelry industry the quantity of gold must be at least 1/20th by weight of the total product.