Rouille (pronounced: [ʁuj], French 'rust') is a sauce that consists of olive oil with breadcrumbs, garlic, saffron and chili peppers. It is served as a garnish with fish, fish soup and, notably, bouillabaisse. Rouille is most often used in the cuisine of Provence.
See also 
- Sharon Tyler Herbst. The New Food Lover's Companion, Second Edition. 1995. Cited in the Food Network Encyclopedia entry for 'rouille'.