Gold is a precious metal that is very soft when pure and is the most malleable and ductile - that is able to be made into wire, metal.
24 karats denotes 100% pure gold, but it is usually alloyed to make it less expensive and harder.
Any karat value below 24 is the amount of pure gold that occupies the gold jewelry alloy. For example, 18 karat equals 18/24ths of pure gold which is 75% gold.