Learn in the textbookRequirements Definition and Design
DefinitionQuality characteristics (品質特性) sort software quality into viewpoints, such as how easy it is to use and how rarely it fails.
ExplanationThe JIS X 25010:2013 standard divides quality into 8 characteristics, while earlier standards used 6. Functionality in the earlier standard roughly matches functional suitability in JIS X 25010. Splitting a vague sense of "good quality" into viewpoints makes targets easier to set when defining requirements, and lets the finished product be judged viewpoint by viewpoint.
AnalogyIt is like a scorecard that rates a car item by item: fuel economy, ride comfort, few breakdowns, and ease of servicing.