“Some people think luxury is the opposite of poverty,” said Coco Chanel. “It is not. It is the opposite of vulgarity.” The late Jean-Louis Dumas, who headed Hermès for 28 years, didn’t like the word “luxury,” thinking it arrogant. He spoke instead of “refinement.” So the definition of luxury is flexible. Is it extravagance in design? Materials? Technical polish? Purity? Expense? This exhibition, curated by Olivier Gabet and comprised of objects from the Musée des Arts Décoratifs, the Louvre, and other institutions from across the globe, offers answers. —J.V.