Define the term "film noir."

The term "film noir" is indeed best defined as a style characterized by dark themes and moral ambiguity. Film noir emerged primarily in the 1940s and 1950s, and it often portrays a cynical worldview, exploring complex characters placed in morally ambiguous situations. The narratives typically involve crime, psychological tension, and a sense of impending doom, often accompanied by a visual style that incorporates low-key lighting, stark contrasts, and an overall atmospheric mood.

This genre is notable for its focus on the flawed, anti-heroic characters who navigate a treacherous moral landscape, highlighting the darker aspects of human nature and society. The aesthetic and thematic elements found in film noir have influenced many subsequent genres and styles, making it a significant movement within cinematic history.

The other definitions do not align with the essence of film noir; a focus on bright themes, musical elements, or solely visual effects misses the depth and complexity that characterize this particular genre.