Glycerol (or glycerin, glycerine) is a simple molecule. It is a colorless, odorless, thick liquid that is widely used during the last step of preparing prescription drugs. Glycerol has three hydrophilic (water-loving) hydroxyl (oxygen-hydrogen) groups that are responsible for its solubility in water and its hygroscopic nature (which means it attracts water from the air). The glycerol backbone is central to all lipids known as triglycerides. It is used is in making nitroglycerin.