What is Hue and Saturation?
Hue is the main indication of color. It is the value actually telling you which color it is or the value that lets you go "red" when you see a red object.

Saturation is the perceived intensity. In other words it is a value of how dominant the color is, or how colorful the object looks.

Practical example: Regardless of the color, shadows generally happen to have low saturation values.