Soap is a substance used for cleaning and washing objects or people. It is solubile in water, but also dissolves and loosens grease or oil molecules that are stuck to a surface, which is the reason for its cleaning powers.
Soap is not toxic, but has an unpleasant taste. This is one of the reasons why mouthsoaping is used as a punishment. Soap also irritates the eye and is very painful if it accidentally gets in your eye, which can easily happen when shampooing.
Soap can also be used to stiffen cord for whip-making.