Major depressive episode

A period of at least two weeks marked by depressed mood or loss of interest, additional depressive symptoms, and clinically significant distress or impairment.

Depressed mood: A sustained feeling of sadness, emptiness, or hopelessness. It is one of the two core symptoms that can define an episode.
Stress-diathesis model: A framework in which vulnerability and stressors interact to influence the onset of disorders. It explains how predisposition and life events can combine before an episode.
Persistent depressive disorder: A chronic depressive disorder involving depressed mood for at least two years in adults. It differs chiefly in chronicity, though episodes can occur within its course.
Major depressive disorder: A depressive disorder involving one or more major depressive episodes and no history of mania. An episode is a defining component used to diagnose this broader disorder.
Functional impairment: A limitation in carrying out important activities or roles because of health problems. Work, relationships, and self-care may be impaired during an episode.
Anhedonia: A reduced ability to experience interest or pleasure in activities. Loss of interest or pleasure is the other core symptom that can define an episode.
Hypothalamic–pituitary–adrenal axis: A hormonal system linking the hypothalamus, pituitary gland, and adrenal glands in the stress response. Stress-system activity is studied as one possible contributor to depressive symptoms.
Bipolar disorder: A mood disorder defined by episodes of depression and mania or hypomania. A history of mania or hypomania changes the diagnostic interpretation of depression.
Depression screening: The use of brief tools or questions to identify people who may need further depression assessment. Screening can flag symptoms but cannot establish an episode diagnosis by itself.
Depression relapse: The return of depressive symptoms after improvement or remission from an episode. Relapse is a key concern after symptoms have eased.

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