What does "naphthol" mean?

Naphthol: Any one of a series of hydroxyl derivatives of naphthalene, analogous to phenol. In general they are crystalline substances with a phenol (carbolic) odor. Naphthol blue, Naphthol orange, Naphthol yellow (Chem.), brilliant dyestuffs produced from certain complex nitrogenous derivatives of naphthol or naphthoquinone.