Fat triglyceride molecules have more hydrogen on their fatty acids and are usually solid at room temperature. Which type of fatty acid (saturated or unsaturated) is more common in fat triglycerides?
the term "saturated" refers to the ratio of hydrogen to carbon atoms - if all carbons in the chain are connected by single bonds, this will maximize the ratio, saturating the molecule with hydrogen.
for every double bond between carbon atoms, two fewer hydrogens will be able to bind to the chain (as two bonding sites get used up when the carbons bond to one another). This also locks the geometry of the bond, causing the straight chain to kink in one of two directions (Cis or Trans). These twisted chains don't stack neatly and this results in an unsaturated fat molecule that typically would be a liquid at room temperature.