Hi there!

Saturated fatty acids have only single covalent bonds present between each of its constituent element. While an unsaturated fatty acid has multiple (double or triple) bonds between some of its elements along with the single bonds. 

Saturated fatty acids solidify at room temperature while unsaturated fatty acids remain liquid at room temperature.

For detailed explanation of the topic, visit the following link:

https://youtu.be/VJmyugWKIOw?t=2819

Thanks