Gold-plated jewelry is exactly what it sounds like. It's made of base metal with a very thin layer of 1% real gold applied to the surface through an electric current, giving it the appearance of being gold without spending as much money.
Essentially, gold-plated jewelry is the same thing as vermeil jewelry, only the base metal is usually of a lower quality than silver, such as copper or brass. Also, gold-plated jewelry is less expensive than vermeil, as it doesn't require a minimum karat weight or thickness. However, a gold-plated item might be more valuable than a vermeil one with a high gold karat weight (20 or 22k) and a thick layer of gold.
Gold plated pieces usually have an intense yellowish hue. However, it can wear off over time.