What part of speech is “depression”

'depression' is a noun that defines a state of low mood and aversion to activity that can affect a person's thoughts, behavior, feelings and sense of wellbeing. It can lead to physical symptoms such as difficulty sleeping, eating, and concentrating, as well as emotional symptoms such as a feeling of sadness and hopelessness.

The depression she experienced after her breakup was very difficult to cope with.

The economic recession caused a nationwide depression in the job market.

The recent studies of clinical depression in children have shown alarming trends.