Calcium oxide (CaO), also known as quicklime, is an alkaline substance which has been in use since the medieval age. It is believed that quicklime is one of the oldest chemicals known to the human race. It can also be referred to as burnt lime.
The broadly used term "lime" connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate.
Calcium oxide can be produced by thermal decomposition of materials like limestone.