When people talk about the "Chroma" of a colour, they can be talking about one of two things, they are either referring to the purity and intensity of the colour or how saturated it is, but both terms are independent of each other as they both have a different meaning.
The "Pure" colours in the Alpha range, with the exceptions of the Oxides and White, such as Pure Green and Pure Magenta have a high Chroma value. What this means is that the colours are rich, full and have really high tinting properties with a poor hiding power or a higher transparency.
Colours like Pure Oxide Red appear duller or pale in comparison and are classed as having a low Chroma value, they have a lower tinting strength which means that they don't adjust colours as readily, but have superior hiding power making them great for adding body to colours.
If you've ever wondered why a Yellow sometimes covers really well, it's likely to have had a low chroma Pure Oxide Yellow mixed with a high chroma Pure Yellow pigment. This leads nicely onto the term Saturation.
Saturation is a secondary term that sits alongside Chroma. If you looked at a colour wheel, fully saturated colours sit on the outer edge of the wheel while fully desaturated colours sit at the centre.
The "Chroma" of the colour means very little here, Saturation just means is just how much of the primary hue there is, the moment you mix in a secondary or tertiary hue, the Saturation reduces accordingly.