Major Depressive Disorder (MDD):A more severe form of depression that involves persistent feelings of sadness, hopelessness, and a loss of interest in activities, often accompanied by physical symptoms and significant impairment in daily functioning.
Persistent Depressive Disorder (PDD): The current diagnostic term for dysthymia, which encompasses both chronic, low-grade depression and more severe, episodic major depression.
Mood Disorder: A broad category of mental health conditions characterized by persistent and pervasive disturbances in mood, including depression and bipolar disorder.