14k gold-filled is a solid layer of 14k gold that has been pressure bonded unto a base of quality jewelers brass. Gold filled is legally required to be at least 5% gold, which is significantly more (easily 100x more) than gold plated items which are often only have 0.05% gold.
Gold-filled is durable and will never rub or flake off. It has a thick layer of solid 14k gold that offers a wonderful, quality piece without paying the solid 14k gold price. It is the next best thing, in terms of quality and durability, to solid gold jewelry.
If your gold-filled jewelry ever develops a tarnish, it is usually a surface tarnish which can be cleaned or polished off. For more info on cleaning, you can click here.