NH4OH, or ammonium hydroxide, is a chemical compound formed when ammonia gas (NH3) dissolves in water. It is often represented as a solution of ammonia in water and is commonly used in cleaning products due to its ability to dissolve grease and dirt. In its pure form, NH4OH is a weak base and can be found in various household and industrial applications. It is important to handle it with care, as concentrated solutions can be irritating to the skin and eyes.