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).
  The term lipid commonly refers to fats, which are known chemically as triglycerides. Triglycerides are organic molecules that contain three different types of elements â¦ : carbon, hydrogen, and oxygen. But technically, lipids are a class of molecules that includes triglycerides, phospholipids, steroids, and waxes.So if you wanted to know what elements are found in lipids as a class, you'd have to allow for phosphorus as well, since phospholipids contain phosphorus in addition to carbon, hydrogen, and oxygen.ut technically, lipids are a class of molecules that includes triglycerides, phospholipids, steroids, and waxes. So if you wanted to know what elements are found in lipids as a class, you'd have to allow for phosphorus as well, since phospholipids contain phosphorus in addition to carbon, hydrogen, and oxygen.