Definition of film noir:

The term film noir describes a type of film that is very dark in its outlook. The word noir is French for 'black', and it was during the 1940s that film noir came into its own. The term was coined by film critics just after World War II. 
Film noir is the flip side of life. Doomed heroes, manipulative people and hidden personal and political agendas are around every corner. The lighting used in film noir is very dark, creating long shadows and claustrophobic atmospheres that pervade the films. The characters in film noir of the 1940s always seemed to be set in dark, smoke filled rooms, like flies trapped in spider webs.
Important Note: Strictly speaking, film noir is not a genre, but rather the mood, style, point-of-view, or tone of a film. It is also helpful to realize that 'film noir' usually refers to a distinct historical period of film history - the decade of film-making after World War II, similar to the German Expressionism or the French New Wave periods. However, it was labeled as such only after the classic period - early noir film-makers didn't even use the film designation (as they would the labels "western" or "musical"), and were not conscious that their films would be labeled noirs

The lighting in film noir is very different to other films from any genre, it is very dark and figures of people are usually seen by candle light, lamp posts, torches and other lights which only show areas of the scene instead of a full on view of the whole scene and what is happening. Often the light will be shining through a layer of smoke witch is often from the actors smoking cigarettes to create the hazy, smokey look which is expected by the audience watching a film noir movie.  

The typical characters in a film noir movie are;
- The anti-hero; the character that is trying to help the situation and people the other characters but he has a flaw which could be personal or could be a bad past. The anti-hero usually gets involved with the femme-fatal who will get him into trouble then he will realise he should have been with the girl next door instead and had a happy life with her. In the ending he will die or end up locked away in prison.
- The femme-fatal; the character that is medelling in the situation having the anti-hero wrapped around her finger. She is usually a 'sexy' women who always wears high heels and red lipstick to get men to do what she likes. She often has money with a blunt attitude and is in a high position with control.
- The girl next door; the character that is very innocent compared to all of the other characters in film noir. She is usually a pretty and plain women who has a normal background and life with her nice family around her. She is what the anti-hero really wants to help sort his life out but he does not realize until after experienced the femme-fatal's games. 
- The villan; the character that is the cause of all of the bad situations happening in the film and the character the anti-hero is trying to catch or kill. He is usually shown as a man who is mysterious and distant with no friends or family around to care about him, he will usually end up dead or in prison.

The plot for film noir is always a Crime, usually murder. greed and jealousy is frequently the criminal motivation. A crime investigation by a private eye, a police detective or a journalist is the most common way of gaining justice in film noir. In other common plots the protagonists are usually in heists or con games, or in murderous conspiracies often involving adulterous affairs. False suspicions and accusations of crime are frequent plot elements, as are betrayals and double-crosses.

Setting; Film noir is often associated with an urban setting, and a few cities such as Los Angeles, San Francisco, New York, and Chicago, in particular which are the location of many of the classic films. In the eyes of many critics, the city is presented in noir as a "labyrinth" or "maze".Bars, lounges, nightclubs, and gambling dens are frequently the scene of action. The climaxes of a substantial number of films noir take place in visually complex, often industrial settings, such as refineries, factories, trainyards, power plants—most famously the explosive conclusion of White Heat, set at a chemical plant.