Karat is a word, usually abbreviated with the letter "K" which describes a unit of measurement determining the purity of metals; most often gold. The term karat is combined with a number usually ranging from 10 to 18, the higher the number, the higher the purity of gold.
Gold, by nature is a soft and pliable metal. Before it may be made into a solid piece of jewelry, it must be combined with a certain measurement of a stronger metal to help retain its shape and strength. This process of combining the atoms of gold with the atoms of another metal is called making an "alloy."
A high percentage of gold is signified by a higher karat. As a result, 24k is the unit that describes pure, 100% gold. Therefore 12k is a 50/50 ratio between gold and another metal. Anything less than 12 karats contains more of the alternate metal than gold.
9K Gold vs. 14K Gold
Any alloy containing 9k gold has only a minor percentage "real" gold and for most jewelers is not actually considered "gold" at all. On the other hand, 14k has more real gold than it has its alternate metal counterpart and the higher purity comes with a higher price tag.