Colorimetry: Gamma/gamut colors Color/color light
As you might know, there are different colour schemes/models available (RGB, HSL, HSV etc) and the important thing to notice is that these schemes are equivalent, which means you can achieve 
exactly the same colour manipulations using any of the schemes. Why do we have different schemes then? It's because some things are (much) simpler to do using a scheme designed for a particular purpose. 

The hue, saturation and lightness/luminance parameters are a part of the HSL colour scheme. The three parameters together define a colour. It's the luminance parameter that defines the lightness.
This particular scheme  makes it extremely easy to create effects such as colour gradients. The only parameter to change is,of course, the luminance.

As an example, let's say that we want to create a gradient from red to white. In the RGB colour scheme, red is encoded as (255,0,0) and white is (255,255,255). As you can see, both the green and blue components have to be changed 
in order to create the gradient. 

In contrast, in the HSL scheme red is encoded as (0,255,0) and white is (0,255, 255), which means that we change only the lightness to create our gradient.

To answer your question, all the three parameters constitute a colour whereas only the lighness/luminance defines a colour light.