Definition of SET THEORY. : a branch of mathematics or of symbolic logic that deals with the nature and relations of sets. â set theoretic adjective. See set theory defined for kids. ADVERTISEMENT.
Broadly, the term lipid is encompasses fats (including saturated, monoglyceride, diglyceride and triglyceride), waxes, sterols, phospholipids in the membranes of cells and fat soluble vitamins. Lipid is a basic term representing a molecule that is fat soluble (vs. water soluble).
Lipids are molecules defined by several characteristics, the chief of which is their avoidance of water -- referred to as their nonpolar nature. Lipids are then divided into two categories. One category contains molecules that are long chains of carbon atoms accompanied by hydrogen atoms, such as fatty acids. The other category is molecules in which carbon atoms are attached as multiple ring structures that are fused together, such as cholesterol.