And by definition, a lipid molecule is a biological molecule that is not soluble in water, so it does not dissolve in an aqueous environment. Now, that's because if we study the structure of a lipid molecule, the majority of that lipid molecule consists of a nonpolar hydrophobic section. Now, many of the lipids inside our body and inside other organisms as well, consist of a hydrophobic section known as the fatty acid. So whenever a lipid contains fatty acids, it's the fatty acid component of the lipid that makes it hydrophobic nonpolar. That basically gives it the ability to remain insoluble in an aqueous environment. So, because fatty acids are so dominant and so important, in this lecture, I'd like to focus on what fatty acids actually are, the systematic approach to naming fatty acids, and then discuss some properties of fatty acids and how going from one fatty acid to another fatty acid, the properties may actually change.