depression (from Lat. Deprimo "to press (down), to suppress") is a mental disorder, the main signs of which are reduced - oppressed, depressed, dreary, anxious, fearful or indifferent - mood and a decrease or loss of the ability to receive pleasure (anhedonia).

Depressive mood in some cases can be a normal temporary reaction to life events, such as the loss of a loved one. Depression can be a symptom of certain medical conditions and a side effect of certain medications and treatments; if the cause of depression is not obvious and the depressive disorder occurs without external influences, such depression is called endogenous. With depression, self-esteem is lowered, there is a loss of interest in life and habitual activities. In some cases, the person suffering from it may start to abuse psychoactive substances.