Potassium chloride (also known as KCl or potassium salt) is a metal halide salt composed of potassium and chlorine. Potassium chloride is used to prevent or to treat low blood levels of potassium (hypokalemia). Potassium levels can be low as a result of a disease or from taking certain medicines, or after a prolonged illness with diarrhea or vomiting (see: Wikipedia).