A crystalline salt KNO3 that occurs as a product of nitrification in arable soils, is a strong oxidizer, and is used especially in making gunpowder, as a fertilizer, and in medicine
Potassium nitrate is a dangerous chemical and should be handled with care. You should only use it after you have read ALL the facts, hazards and safety measures. It is an Oxidizer so you should never store it near fire hazards or other chemicals, nor mix it with other chemicals unless you have been trained to.