Non-detergent is a marketing term typically used to describe a type of soap that does not contain synthetic components. Soaps and detergents are both cleaning products, and soaps are generally considered a detergent by definition. However, under FDA regulations, soaps are classified as containing metallic salts of fatty acids.
Normally, soaps are made with an alkali material, such as sodium or potassium, or an alkaline earth metal, such as magnesium or calcium. They are then added to fatty acid of plant or animal origin. Detergents are usually synthetic and contain a sulfate or sulfate group. Detergents are also not inactivated by hard water.