triglyceride
/ try-GLISS-er-ide /
A triglyceride is what we mean in everyday life by 'fat' or 'oil' — the butter on toast, the oil in a frying pan, the fat stored under your skin. Chemically it is one of the tidiest molecules in biochemistry: a single molecule of glycerol with three fatty acids attached. That is the whole story — glycerol provides three hydroxyl groups, and each one is esterified to a fatty-acid tail.
Glycerol is a small three-carbon molecule with an -OH on each carbon (HOCH2-CHOH-CH2OH). A triglyceride forms when each of those three hydroxyls reacts with the -COOH of a fatty acid to make an ester, releasing three molecules of water. The result looks like a capital E lying on its side: a short glycerol spine on the left, three long fatty-acid tails fanning out to the right, joined by three ester linkages. This is nothing more than Fischer esterification done three times, and it can be undone three times: hydrolyze the esters and you recover glycerol plus three fatty acids; hydrolyze them with sodium hydroxide instead and you get glycerol plus three fatty-acid salts, which is soap (saponification).
Triglycerides matter because they are the body's main long-term fuel and the bulk of dietary and stored fat. Whether one is a solid 'fat' or a liquid 'oil' depends entirely on its tails, just as for the free fatty acids: saturated tails pack tight and stay solid at room temperature (animal fats), while cis-unsaturated tails kink and stay liquid (plant oils). They are the textbook payoff of ester chemistry — three esters on one tripod, and the difference between lard and olive oil comes down to which fatty acids fill the three slots.
Boiling a fat (a triglyceride) with NaOH cleaves all three ester bonds at once: you get one glycerol and three fatty-acid carboxylate salts — soap. This is saponification, and it is exactly the base-promoted ester hydrolysis you already learned, run three times on one molecule.
A triglyceride is just three esters on one glycerol; saponification hydrolyzes all three into soap.
'Fat' (solid) versus 'oil' (liquid) is purely about how saturated the tails are, not a difference in kind — both are triglycerides. And blood 'triglycerides' on a lab report are these same molecules, not a separate substance.