About this term
Source: Oxford University Press
Finely powdered colouring matter that is suspended in a binding medium to form paint; for pastel (see Pastel, §1) the pigment is moulded into sticks with the aid of a binding medium. In most forms of painting the binding medium, which may be oil, egg yolk, water or a variety of other substances, holds the pigment particles together and attaches them to a surface. In Fresco painting, however, the pigments are mixed with water for application, but when dry they form an integral part of the surface of the plaster.
From Grove Art Online