The word depression comes from the Latin depressus, meaning killed or overthrown. It is an emotional disorder that appears as a state of despair and unhappiness that can be transient or permanent.

For medical and psychological science, depression is a syndrome or a cluster of symptoms that primarily affect the affective area of a person. Thus, pathological grief, decay, irritability and mood disorder may cause a decrease in job performance, academic, social and family of a person.

Some of the features of depression is that the person may not experiencing sadness, but loss of interest and inability to enjoy normal play activities, and a little experience motivating and slower over time. Its origin is multifactorial, although it is noted triggers such as stress and feelings (derived from a disappointment in love, contemplation or experience of an accident, murder or tragedy, the bad news disorder, grief, and having gone through an experience near-death). There are other sources, such as inadequate elaboration of mourning (for the death of a loved one) or even the consumption of certain substances (alcohol or other toxic substances) and predisposing factors such as genetics or educational status. Depression can have important social and personal consequences, from incapacity to suicide.

There are several types of depressive disorders. The three most common types of depression are: Major Depressive Disorder, Dysthymic Disorder and Bipolar Disorder. In each of these three types of depression, the number, severity and persistence of symptoms vary.

When a person's psychic situation involves a limitation on their activities and it stops functioning, affecting their quality of life, therapeutic treatment is recommended, which ends when a person improves their psychic situation and manages to reestablish the normal functioning of biopsychosocial skills.