labrys edge's has done well in communicating the basics of clinical depression in her writeup. Most of the information appears to have come from www.clinicaldepression.com. Some additional information will be helpful, I believe. In clinical practice, the term "clinical depression" almost alway refers to the condition described by the above listed symptoms, and caused by one or more neurotransmitter deficiencies. There is often a stigma attached to "depression". This is due to the lack of differentiation between "clinical depression" and "major depression".
Helping people understand clinical depression:
The first thing that helps people come to grips with this condition is differentiating the condition from the symptoms. If you explain it by comparing it with diabetes, where the disease is the sugar imbalance, and the symptoms are the drowsiness, weight gain, blurry vision, etcetera, then people have something more familiar with which to compare the depression. This also helps them understand that the symptoms aren't somehow their fault. Most commonly, a history of family members with conditions that signify a predisposition toward imbalances of neurotransmitters can be elicited. Asking a depressed person if they have any family members or close relatives with depression, alcoholism, "nervous breakdowns", or suicide attempts will very frequently bring a positive response, and this can help them understand that it is a medical condition, not a psychiatric one.
The second thing that helps is explaining what clinical depression is not, and that is major depression. I really wish that whoever came up with this term hadn't. It would be much better referred to as "clinical dysthymia/dysphoria" or "serotonin deficiency syndrome". The confusion with major depression is unfortunate. Explaining briefly that major depression is a psychiatric disorder, brought on by strong conditioning in a person's past that predisposes them to see the world, events, or their chances of happiness or success in life in a negative or pessimistic way, helps to distinguish it from the medical condition. (There is much more to major depression - it is basically that, but much more complex.)
The more information people have about their condition, the better the success rate in treating that condition. The recent study results relating the surprising lack of improved efficacy of antidepressants vs. placebo is, in my opinion, a reflection of the over-prescribing of good medicine for conditions that are truly not clinical depression. Used appropriately by experienced clinicians, the current medications for depression have show very good results in treating this condition, and I would encourage anyone who feels like they may be suffering from clinical depression to seek reputable medical help to see if treatment is appropriate for them.