Gold Filled: Gold Filled jewelry is made by wrapping layers of solid gold (14K, 12K, or 18K) sheets around a base metal (usually brass). Unlike gold plated jewelry, gold filled jewelry actually has a measurable amount of gold in it (5%).
This process of adhering solid gold sheets makes for jewelry that does not tarnish, peel, chip or discolor. If your gold-filled jewelry has ever changed color at all its usually just because of dirt build up and can be cleaned with a damp cloth. Also, unlike silver, it won't tarnish.
Because gold filled jewelry is made with solid gold sheets, the base metal will not come in contact with the skin. This makes it a safe metal for people with sensitive skin. On the other hand, gold plated jewelry has such a tiny, almost not existent layer of gold that base metal comes in contact with the skin and often causes irritation.
Gold Plated: The process of gold plating is one where a minuscule layer of gold is applied over a base metal (usually brass). The amount of real gold that is used is actually so tiny that its technically considered unmeasurable (less than .05%). This is why gold plating will wear off (actually pretty quickly).
