Saturation is proportional to the freezing or melting point of lipid structures (e.g. oils).
Here, coconut oil will freeze before sunflower oil because coconut oil is more saturated with hydrogen atoms bonded to its hydrocarbon chain.
To answer sheetal-sinha's question:
Saturation refers to the amount of hydrogen atoms bonded to the hydrocarbon chain that makes up most lipids. If a double bond forms for instance, it will have less hydrogen atoms bonded and become unsaturated.