This is one of the ways of describing a colour, along with 'Brightness' and 'Saturation'. Hue, Saturation and Brightness can fully define a particular colour.
Hue is the *main* colour of something (such as a pixel, or a light source).
For example you would say 'that is a red light'. The hue is 'Red. On the other hand you might say 'That is a reddish light' by which you mean you sense the colour being mainly red, but it is mixed up with some other colours as well.
On a standard colour wheel, Hue is describing the angle from the top of the wheel. Saturation is the distance of that colour from the centre of the wheel and Brightness is the relative strength of the colour. If a colour is right at the edge of the wheel then you would say it is fully saturated and appears very pure.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: Hue