Definition:
Film noir (literally 'black film or cinema') was coined by French film critics who noticed the trend of how 'dark', downbeat, and black the looks and themes were of many American crime and detective films released in France to theaters following the WWII.
The classic noir story:
A cynical, hard-hearted, disillusioned male character encounters a beautiful but promiscuous, amoral, double-dealing and seductive femme fatale. She uses her feminine sexuality to manipulate him. After a betrayal or double-cross, she is frequently destroyed as well, often at the cost of the hero's life.
Typical noir moods:
melancholy
bleakness
disillusionment
ambiguity
moral corruption
guilt
desperation
paranoia
The classic noir anti-hero:
corrupt
down-and-out
conflicted
hard-boiled
morally-ambiguous
cynical
obsessive (sexual or otherwise)
brooding
menacing
frightened
The typical noir story line:
elliptical
non-linear and twisting
maze-like and convoluted
typically told with foreboding background music and flashbacks
often told with witty dialogue, and/or reflective and confessional, first-person voice-over narration.
Typical noir themes:
the dark and inhumane side of human nature
doomed love
emphasized the brutal, unhealthy, seamy, shadowy, dark and sadistic sides of the human experience