Is depression a lack of emotion?

No: Depresion characterizes for feelings of profound sadness or guilt which may lead to insomnia or excessive somnolence, lack of energy, fatigue, loss of weight or excessive weight, loss of appetite or excessive eating, crying often, desire to die or kill, multiple aches and pains and non specific symptoms, loss of interest - in hobbies, in sex or low libido, or in activities that previously liked--.

Can be: Clinical depression can involve a lack of joy or emotional blunting; it can also include a persistent and pervasive period of sadness, excessive guilt or apathy, difficulties getting motivated, poor concentration and energy, disrupted sleep, feelings of sluggishness or restlessness, social withdrawal, and/or thoughts of death. It is very treatable by seeking medical care.

Depression: Emotional numbing can be a component of depression, or severe trauma. Numbing (lack of emotion) is a defensive suppression of emotion, not lack thereof. Other components of depression include blue mood, lethargy, anger, hopelessness, social isolating, and sleep/appetite disturbances.