What is Genre in film?

Movie genres are stylistic categories which a certain movie can be placed depending on the setting, characters, tone, plot,mood and theme. A films main genre will be based on where the majority of the content land. There is also such things as a subgenera which is a smaller category which fits inside a bigger genre. Mostly this a mixture of two different genres.

So what is the definition of the thriller genre?

The thriller genre is characterised and defined by the moods the elicit, giving viewers heightened feelings of suspense, excitement, surprise, anticipation and anxiety.

Setting

Setting is the time and place of a story, which can be outwardly articulated to us, or discreetly suggested to us. Factors which can suggest setting include weather, clothing, culture, architecture, etc. Setting could be a character which affects how we experience the story from within a film. Setting often specifies which genre a film might fall into. If there is a lack of intention with setting in a film, it can weaken a story and the audience experience of the film. Therefore this an entire department which their main job is to focus on fleshing out the details of a story setting. This is called the art department, they are in charge of production design in a film; this directly affects the setting. 

Characters

Films always need a character to execute the experience. Characters typically tell the story and are a tell-tale sign of a film genres. This can be through not only physical characteristics but internal characteristics as well. A characters desires, behaviour, or personality may lend itself to a specific genre.

Theme

Every good film has a central topic or message in the story. This is called a films theme. It is often the spine of a story as it is essentially what the audience will walk away with. However just because there are different genres that doesn't mean that they can't carry the same theme. For example, a poor film can undoubtedly by be cliche, a great film can be a classic.