This is a useful article breaking down some of the signs of depression. Knowing what depression is can be proved useful to address what might be affecting ones wellbeing. The diagnosis of depression though can lead to other issues such as overprescribing medications without first exploring other available interventions. Depression has a vast spectrum and it needs to be approached with sensitivity. Being informed about what depression really entails is the first step for a thoughtful treatment.
http://www.theguardian.com/lifeandstyle/2015/jan/21/are-you-depressed-without-knowing-it