A habitué is a frequent and well-known patron of a particular place. If you walk into a restaurant, and the entire staff waves and says your name, you are likely a habitué.
The English habitué is spelled and pronounced the same as the 200-year-old French word (the accent is optional), which means "accustomed." The most famous habitué in American sitcom history is probably Norm Peterson of Cheers, whose arrival was always greeted by a chorus of patrons shouting "Norm!" Other, less French-sounding words for this famous fellow might be fixture or regular.