An establishment where people can come in and order a meal of their choice off a menu, then a waiter or waitress sends the order to the kitchen where a chef and his/her team prepare said meal. The server then returns to the table with the dish, and then the customer pays for it after finishing. This is a very popular business because most people do not have the time to make meals on their own, or don't do it as well as the restaurant does.
Restaurants exist for all three different meals through the day - breakfast, lunch and dinner - and for any type of palette, whether it's American, Japanese, Chinese, Mediterranean and so on. There are also late night and 24/7 places for those who work during the night.