A visual tone that reduces contrast, motion, and visual competition to create a calm, unobtrusive interface: one that doesn’t demand attention.
The reading view strips away navigation and uses a quiet typographic treatment so nothing competes with the text.
Quiet is not the same as minimal. Minimal is about quantity: fewer elements. Quiet is about volume: lower intensity. You can have a complex interface that is still quiet. Notion is quiet. Linear is minimal.