Wikipedia:White House chefs preparing the official dinner for the Prince of Wales and the Duchess of Cornwall.
A chef is a person who cooks professionally for other people. Traditionally it refers to a highly skilled professional cook who is proficient in all aspects of food preparation.
The word "chef" is adopted (and shortened) from the term chef de cuisine (French pronunciation: [ʃɛf.də.kɥi.zin]), the director or head of a kitchen. (The French word comes from Latin caput and is a doublet with English "chief".) In English, the title "chef" in the culinary profession originated in the haute cuisine of the 19th century. Today it is often used to refer to any professional cook, regardless of rank, though in most classically defined kitchens, it refers to the head chef; others, in North American parlance, are "cooks".
Below are various titles given to those working in a professional kitchen and each can be considered a title for a type of chef. Many of the titles are based on the brigade de cuisine (or brigade system) documented by Auguste Escoffier, while others have a more general meaning depending on the individual kitchen.
Chef de cuisine, executive chef and head chef 
This person is in charge of all things related to the kitchen, which usually includes menu creation, management of kitchen staff, ordering and purchasing of inventory, and plating design. Chef de cuisine is the traditional French term from which the English word chef is derived. Head chef is often used to designate someone with the same duties as an executive chef, but there is usually someone in charge of them, possibly making the larger executive decisions such as direction of menu, final authority in staff management decisions, etc. This is often the case for chefs with multiple restaurants.
The Sous-Chef de Cuisine (under-chef of the kitchen) is the second-in-command and direct assistant of the Chef de Cuisine. This person may be responsible for scheduling the kitchen staff, and substituting when the head chef is off-duty; he/she will also fill-in for or assist the Chef de Partie (line cook) when needed. This person is accountable for the kitchen's inventory, cleanliness, organization, and the ongoing training of its entire staff. A sous-chef's duties can also include carrying out the head chef's directives, conducting line checks, and overseeing the timely rotation of all food product. Smaller operations may not have a sous-chef, while larger operations may have more than one.
Chef de partie 
A chef de partie, also known as a "station chef" or "line cook", is in charge of a particular area of production. In large kitchens, each station chef might have several cooks and/or assistants. In most kitchens, however, the station chef is the only worker in that department. Line cooks are often divided into a hierarchy of their own, starting with "first cook", then "second cook", and so on as needed.
Commis (Chef) 
A commis is a basic chef in larger kitchens who works under a chef de partie to learn the station's responsibilities and operation. This may be a chef who has recently completed formal culinary training or is still undergoing training.
Station-chef titles which are part of the brigade system include:
Kitchen assistants 
Kitchen assistants are of two types, kitchen-hands and stewards. Kitchen-hands assist with basic food preparation tasks under the chef's direction. They carry out relatively unskilled tasks such as peeling potatoes and washing salad. Stewards are involved in the scullery, washing up and general cleaning duties. In a smaller kitchen, these duties may be incorporated.
A communard is in charge of preparing the meal for the staff during a shift. This meal is often referred to as the staff or family meal.
The escuelerie (from 15th century French and a cognate of the English "scullery"), or the more modern plongeur or dishwasher, is the keeper of dishes, having charge of dishes and keeping the kitchen clean. A common humorous title for this role in some modern kitchens is "chef de plonge" or "head dishwasher".
Culinary education 
United States and Canadian training 
Culinary education is available from a wide number of institutions offering diploma, associate, and bachelor degree programs in culinary arts. Depending on the level of education, this can take one to four years. An internship is often part of the curriculum. Regardless of the education received, most professional kitchens follow the apprenticeship system, and most new cooks will start at a lower-level 2nd or 1st cook position and work their way up.
European training 
The training period for a chef is generally four years as an apprentice. A newly qualified chef is advanced or more commonly a torquecommis-chef, consisting of first-year commis, second-year commis, and so on. The rate of pay is usually in accordance with the training status. Commis chefs, like all other chefs except the executive-chef, are placed in sections of the kitchen (e.g., the starter (appetizer) or entrée sections) under the guidance of a demi-chef de partie and are given relatively basic tasks. Ideally, over time, a commis will spend a certain period in each section of the kitchen to learn the basics. Unaided, a commis may work on the vegetable station of a kitchen.
The usual formal training period for a chef is two to four years in catering college. They often spend the summer in work placements. In some cases this is modified to 'day-release' courses; a chef will work full-time in a kitchen as an apprentice and then would have allocated days off to attend catering college. These courses can last between one to three years.
The standard uniform for a chef includes a hat, necktie, double-breasted jacket, apron and shoes with steel or plastic toe-caps. A chef's hat was originally designed as a tall rippled hat called a Dodin Bouffant or more commonly a toque. The Dodin Bouffant had 101 ripples that represent the 101 ways that the chef could prepare eggs. The modern chef's hat is tall to allow for the circulation of air above the head and also provides an outlet for heat. The hat helps to prevent sweat from dripping down the face. Neckties were originally worn to allow for the mopping of sweat from the face, but as this is now against health regulations, they are largely decorative. The chef's neck tie was originally worn on the inside of the jacket to stop sweat running from face and neck down the body. The jacket is usually white to show off the chef's cleanliness and repel heat, and is double-breasted to prevent serious injuries from burns and scalds. The double breast also serves to conceal stains on the jacket as one side can be rebuttoned over the other.
An apron is worn to just below knee-length, also to assist in the prevention of burns because of spillage. If hot liquid is spilled onto it, the apron can be quickly removed to minimize burns and scalds. Shoes and clogs are hard-wearing and with a steel-top cap to prevent injury from falling objects or knives. According to some hygiene regulations, jewelry is not allowed apart from wedding bands and religious jewelry. If wound dressings are required they should be blue—an unusual colour for foodstuffs—so that they are noticeable if they fall into food. Facial hair and longer hair are often required to be netted, or trimmed, for food safety. Bandages on the hands are usually covered with latex gloves.