Vitamin K is a vitamin used to regulate the body's clotting process (from where it gets its name from the German Koagulations), bone metabolism and maintenance of blood vessels. It's found in most leafy vegetables and some fruits. The body requires very small quantities of the vitamin - a tablespoon-and-a-half of parsley contains enough to meet a body's daily needs. The body can also extract Vitamin K from meat and dairy products when these are digested by bacteria in the intestines.
Vitamin K deficiency is very rare. Not only is Vitamin K plentiful in most diets, large quantities can be stored in fat and the vitamin is rarely expelled from the body (it is usually recycled, unlike Vitamin C and other vitamins which are continuously removed from the body). Deficiency is usually caused by the failure of the body's processes for extracting the vitamin rather than a lack of the vitamin in the diet.