What does gold plated mean?

Plated means metal on top of metal. The most important is the base metal, especially if your skin is allergic to any. The base color may also peek through as plating wears off. Base metals can be silver, copper, brass.
The plated metal on top can be any karat of gold.
If you're looking to wear this type of chain every day, the plating will wear off quicker. We suggest you avoid all moisture. This includes lotions, sprays, showering, pools. 
Some people don’t mind wear n tare simply because it is plated or it was a gift. Companies may offer a warranty for tarnishing on your plated piece. It is ultimately up to you to take care of plated jewelry to make it last as long as you need it to.