Besides the lipid vitamins that are fat-soluble, hormones, waxes, oils, and many very important substances are also examples of lipids. These examples bear little similarity to one another in terms of their chemical formulations. Lipids also vary greatly in their molecular structure. Most lipid molecules are not electrically charged, nor is either end of the compound the least bit electrically polarized. They are non-polar compounds, electrically neutral throughout.
Because there is no structural definition of lipids, the exact definition of a lipid is a bit vague and a few scientists seeking a broad definition will include almost any organic compound that is not water soluble. Many of these can be volatile because their molecules are small. Most scientists do not include mineral oils or waxes obtained from petroleum or paraffin. Instead interest is focused on substances related to living plant and animal biochemistry. And these substances are comprised of large molecules that are non-volatile.
Many lipids are essential to good human health. Some of them serve as chemical messengers in the body. Others serve as ways to store chemical energy. There is a good reason that babies are born with "baby fat." Seeds contain lipids for the storage of energy. People living in Arctic zones seek fatty foods in their diet.
Fat is a poor conductor of heat so lipids can also function as an insulator. Their functions are as varied as their structures. But because they are all fat soluble, they all share in the ability to approach and even enter a body cell.