Cement

Definition:

A cement is a binder, a substance used in construction that sets and hardens and can bind other materials together. The most important types of cement are used as a component in the production of mortar in masonry, and of concrete, which is a combination of cement and
aggregate 
to form a strong building material.

Cements used in construction are usually inorganic, often lime based, and can be characterized as being either hydraulic or non-hydraulic, depending upon the ability of the cement to set in the presence of water.

Non-hydraulic cement will not set in wet conditions or underwater; rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.

Hydraulic cements  set and become adhesive due to a chemical reaction between the dry ingredients and water.The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack.Example:-Portland cement