The base colour itself — red, blue, green, yellow and so on — independent of how light, dark or saturated it is.
The attribute of a colour corresponding to its position on the colour wheel, typically expressed as an angle (0–360°) in HSL, HSV or LCH colour spaces.
People often say 'colour' when they mean hue specifically — 'red' is a hue, but 'pale dusty red' describes hue plus tone and saturation.
Navy blue and sky blue have the same hue (blue) but very different lightness and saturation.
Hue is the first thing most colour relationships (complementary, analogous, triadic) are built from.