Potassium nitrate is commonly known as saltpeter. It is an ionic salt made up of potassium and nitrate ions, with a chemical formula of KNO3. It is famous for being a key ingredient in black powder, which was used as firearm propellant until the 20th century.
Bat guano is a major natural source of potassium nitrate, via immersing the guano in water for a day, and then harvesting the crystals from the filtered water. Today potassium nitrate is used in fertilizer, rocket fuel, fireworks, cigarette production and food preservation.
Popular folklore holds that saltpeter acts as an anaphrodisiac, with the opposite effects of an aphrodisiac, but there is no scientific evidence to support the theory.