According to Web MD, cholecalciferol is commonly known as vitamin D3. It is a fat-soluble vitamin that helps to build and maintain strong bones by aiding in the absorption of calcium and phosphorus. Wikipedia explains that cholecalciferol is an inactive, unhydroxylated form of the vitamin. It is sometimes called calciol.
The body makes vitamin D naturally in response to sunlight. However, as Web MD explains, cholecalciferol is often taken orally as a vitamin supplement to prevent osteoporosis, rickets and other bone disorders. It has no significant side effects, although it does interact with phosphate binders. Because it is structurally similar to cholesterol, it can interfere with cholesterol tests, sometimes causing false results.