In the fields of psychology and psychiatry, the terms<unk> or depressed refer to both expected and pathologically chronic or severe levels of sadness, perceived helplessness,  disinterest, and other related emotions and behaviours. The Diagnostic and Statistical Manual of Mental Disorders (DSM) states that a depressed mood is often reported as being: "depressed, sad, hopeless, discouraged, or 'down in the dumps'." In traditional colloquy, "depressed" is often synonymous with "sad," but both clinical and non-clinical<unk> can also refer to a conglomeration of more than one feeling.  Such a mixture can include (but is not limited to) anger, fear, anxiety, despair, guilt, apathy, and/or grief, in addition to what many people would describe as typical "sadness."
In a clinical setting, a depressed mood can be something a patient reports (a symptom), or something a clinician observes (a sign), or both.
Depression 
Clinical depression
Psychosis
Psychotic depression
Post travel depression
Postnatal depression
Anxiety
Post stroke depression