The higher the Karat number in gold the softer it is.
There are 24 parts to a gold alloy, with each part being 1 karat. So 24k gold is pure gold. 14k gold means that 14 out of 24 parts of the mixture are gold. the other 10 parts are other metals.
Most jewelry is between 14k and 18k. More than 18k is bad because gold is a very soft metal so without enough other metals mixed in, it can break or deform too easily.
9K has less gold per alloy mix, but is stronger and more durable. People that do heavy work with their hands, but still want a gold ring will often choose a 9K ring. It is no less beautiful, but it is stronger.
14k is the ideal mark between purity and durability.