Chroma refers to the purity of a color. A hue with high chroma has no black, white or gray in it. Adding white, black or gray reduces its chroma. It’s similar to saturation but not quite the same. Chroma can be thought of as the brightness of a color in comparison to white.
In design, avoid using hues that have a very similar chroma. Opt instead for hues with chromas that are the same or a few steps away from each other.