Cement is a material for bonding stone or brick. The term cement is most commonly used to refer more specifically to powdered materials which develop strong adhesive qualities when combined with water. These materials are more properly known as hydraulic cements. Hydraulic limes, natural pozzolana and Portland cements are the more common hydraulic cements, with portland cement being the most important in construction. Gypsum plaster and common lime are not hydraulic cements. Cement is an important ingredient in concrete.