Shibui
Refers to a particular aesthetic of simple, subtle, and unobtrusive beauty [1]
“The world abounds with different aspects of beauty. The lovely, the powerful, the gay, the smart—all belong to the beautiful. Each person, according to his disposition and environment, will feel a special affinity to one or another aspect. But when his taste grows more refined, he will necessarily arrive at a beauty which is shibui. Many a term serves to denote the secret of beauty, but this is the final word.”
– Yanagi Soetsu (1889 -1961)
[1] Originating in the Muromachi period (1336–1573) as shibushi, the term originally referred to a sour or astringent taste or “Stimulatingly bitter”. Shibui maintains that literal meaning still, and remains the antonym of amai (甘い), meaning 'sweet'. source wikipedia · among others.