"The product formed by the saponification or neutralization of fats, oils, waxes, rosins, or their acids with organic or inorganic bases"

(American Society for Testing and Materials definition).  This definition of soap covers a wide range of compositions, but in the area of consumer products, soap usually means the sodium or potassium salt of animal fat or a combination of vegetable oil and animal fat.  The principal fats and oils used are tallow and coconut oil.  In common usage, the word soap is also employed generically to describe any washing product that is preponderantly soap or depends on soap for its primary function. Thus toilet and laundry bars, light duty flakes and granules, and all purpose built products are all termed soap, if soap is their base ingredient.  Soap performs its principal task, cleaning, by various mechanisms, including reducing surface tension (it is an anionic surfactant ), loosening, dispersing and suspending particulate soil, emulsifying fatty and oily matter, and providing alkalinity. Soaps are mildly alkaline.  The major drawback to soap, particularly in laundering, is that it forms insoluble lime soap (soap curd) with water hardness minerals, which is deposited on fabrics and in washing machines.  It was this problem that spurred the development of detergents, which are relatively unaffected by hard water and as a result have largely replaced soap for laundry purposes.