From NuGOwiki

The term organic acids refers to a broad class of compounds used in fundamental metabolic processes of the body. Derived from dietary protein, fat and carbohydrate, they are used by the body the generate cellular energy and provide building blocks necessary for cell function. Chemically they share the common features of water solubility, acidity, and ninhydrin-negativity, which means that amino acids are usually excluded from this group. The term is generally considered to include all carboxylic acids, with or without keto, hydroxyl or other non-amino functional groups. Some nitrogen containing compounds are included such as pyroglutamate or amino conjugates like hippurate (benzoylglycine). Short chain fatty acids are also contained in this group.

Source: Natural Medicine (1998), Pizzorno and Murray, churchill Livingstone, London.