Similar to saturation — how far a colour is from neutral grey — but measured in a way that stays consistent across different lightness levels.
In perceptually uniform spaces such as LCH/OKLCH, chroma measures colourfulness relative to a reference white, avoiding some of the lightness-dependent distortion that HSL saturation shows near white or black.
Chroma and saturation are often used interchangeably in casual writing; the technical distinction only really matters when comparing colours across very different lightness levels.
Colourwise's own hue-family and neutral classification uses HSV saturation for simplicity, but its LCH/OKLCH values (shown on every colour profile) report chroma directly.
Chroma is why a pale yellow and a deep red can be described as 'equally colourful' even though their HSL saturation numbers look very different.