"Depression" can refer to different things in different contexts. In everyday language, "depression" is often used to describe a feeling of intense sadness or low mood, which is not a mood disorder but rather a common emotion experienced by many people from time to time.
In clinical terms, "depression" refers to Major Depressive Disorder (MDD), which is indeed a mood disorder. MDD is characterized by persistent feelings of sadness or a loss of interest or pleasure in most activities, along with various other symptoms that significantly impair a person's ability to function in daily life.
However, there is another context in which "depression" is used to refer to a symptom rather than a mood disorder. In this context, depression can be a symptom seen in various medical conditions, such as certain neurological disorders, chronic illnesses, or as a side effect of medications. For instance, people with certain neurological conditions like Parkinson's disease or multiple sclerosis may experience "depression" as a symptom of their underlying condition.
In summary, "depression" can refer to a mood disorder known as Major Depressive Disorder (MDD) or be used as a symptom seen in various medical conditions. However, when discussing depression as a mood disorder, it typically refers to MDD, which is a specific mental health condition characterized by persistent and severe depressive symptoms.