Calcium oxide is a chemical compound with the formula CaO which is a whitish, odorless solid that does not dissolve well in water. It will, however, react with water (H20) to form calcium hydroxide (CaOH, a caustic base). It has a melting point of 2614 degrees Celsius and a boiling point of 2850 degrees Celsius. It can be made by heating calcium carbonate (CaCO3, most commonly limestone) until carbon dioxide (CO2) is released. It is more commonly known as lime or quicklime and has a great many industrial uses, such as:
Some of the information in this writeup was taken from the science dictionary at http://biotech.icmb.utexas.edu/; I oversaw the development of the dictionary (the website was mothballed in 1998) and I believe I wrote the entry this is based on.