Noir: Genre or Style?

We have been taught to that Noir is a genre type, but after careful analysis, one can clearly see that Noir is a style rather than a genre. While the author states: "If you think movies are defined by their themes, then you probably think of noir as a genre. If you define films by their visual look and tone, then to you noir is definitely a style." This raises the question: how do you really define a movie? I agree that Noir is better defined as style. The name it self refers to the dark, shadowy cinematic style.