French term for a wine steward at a restaurant.
Depending on the size and sophistication of the restaurant, the Sommelier may have a variety of responsibilities. At the most basic level, a sommelier (lowercase "s") is in charge of taking wine orders, presenting the bottle, pouring a sample, and keeping diners topped up. A more senior Sommelier (capital "S") would be in charge of the managing the entire wine cellar, tasting and buying wines to match the season and the restaurant's menu. If a restaurant doesn't have the resources to retain a full-time Sommelier, they can use the services of a consultant, who will provide a selection of wines to fit the restaurant's main dishes.
Ultimately, the Sommelier's purpose is to make sure that a diner has the best wine for the food they're eating. They can make the difference between a good meal, and a great one.