Saturation (Color Theory)
In color theory, saturation defines a range from pure color (100%) to gray (0%). Saturation is sometimes referred to as color intensity, a fully saturated color is one of pure color while a fully desaturated color appears as grey. The saturation of a color isn’t constant, it varies depending on factors such as its surroundings and what light the color is seen in.  Saturated colors draw attention due to their brightness and intensity. Using colors with different hues but similar saturation is an effective way to create contrast, when this is properly done the effect is active and intense. 
Saturation in color models
The hue is represented as a degree value from 0° to 360° on a Cartesian grid, with pure red at 0°, pure green at 120°, and pure blue at 240°.
The saturation is a percentage from 0% to 100%, indicating the balance of the pure color and white.
With a hue of pure green (120°), a saturation of 100% is composed of only green light (no red or blue)
(24 bit RGB equivalent – R:0 G:255 B:0).
With a hue of pure green (120°) and a saturation of 0%, the color is white (red and blue increase up to max value)
(24 bit RGB equivalent – R:255 G:255 B:255)
So, sliding the saturation on a primary color up and down the percentage range is equivalent to increasing or decreasing the other two primary colors in equal amounts.
A hue of pure green (120°) with a saturation of 50% then means that the red and green are increased by 50% of their value each.
(24 bit RGB equivalent – R:127 G:255 B:127)
Related terms and definitions
Chroma, intensity, saturation and luminance/value are very related terms which all pertain to the description of a color.
Chroma: The amount of purity hue has relative to gray
Saturation: The degree of purity of a hue.
Intensity: The brightness or dullness of a hue. One may lower the intensity by adding white or black.
- "Color Properties/Terminology". Work With Color. http://www.workwithcolor.com/color-properties-definitions-0101.htm. Retrieved 2014-09-15.
- Schlatter, T., Levinson, D: Visual Usability. Principles and Practices for Designing Digital Applications, 171-211, Morgan Kaufmann, Boston 2013
- Color Basics. (n.d.). Retrieved September 18, 2015, from http://www.worqx.com/color/color_basics.htm