The following linked-to article does a fairly good job of explaining clinical depression.

Clinical Depression Is Not Sadness

The reader should take note of how hard the writer had to work to explain what clinical depression is not – rather than what it is. Many an article attempts to clear up the misunderstanding but leaves the reader with a murky or hybrid comprehension of the disorder.  Sometimes, when we attempt to help others to acquire depth perception on a subject where there is confusion, we try to reorder the building blocks of concepts…creative thinking…but still inside of the box.

The out of box solution for this problematic terminology clinical “depression” is for the medical profession to replace the term altogether – and moreover, cease calling it a mood disorder!

Due Justice Project commented on this problem of the shared language of the common vernacular and psychiatric medical terminology in the article Adding Insult To Injury – How the language of mental illness promotes misunderstanding.  We are living in an age of modern neuroscience but still encumbered with relics of the psychotherapeutic regime of the past. There was a time when the physiological nature of clinical depression was misconceived (and still misconceived by that troublesome faction).

This terminology issue is not a trivial matter. The misleading nature of the term Depression may have tragic implications for those who are experiencing symptoms of the disorder but have not been diagnosed. The writer of this blog has also observed that some people who have the diagnosis do not appear to fully understand their own disorder. Someone who believes that they are experiencing extreme sadness may not seek the medical treatment that they need – a decision that can have deadly consequences.