Depression
Depression may refer to:

Mental health
Depression (mood), a state of low mood and aversion to activity
Mood disorders characterized by depression are commonly referred to as simply depression, including:
Bipolar disorder, also known as manic depression
Dysthymia, also known as persistent depressive disorder
Major depressive disorder, also known as clinical depression

Economics
Economic depression, a sustained, long-term downturn in economic activity in one or more economies
Great Depression, a severe economic depression during the 1930s, commonly referred to as simply the Depression
Long Depression, an economic depression during 1873–96, known at the time as the Great Depression

Biology
Depression (kinesiology), an anatomical term of motion, refers to downward movement, the opposite of elevation
Depression (physiology), a reduction in a biological variable or the function of an organ
Central nervous system depression, physiological depression of the central nervous system that can result in loss of consciousness

Earth science
Depression (geology), a landform sunken or depressed below the surrounding area
Depression (weather), an area of low atmospheric pressure characterized by rain and unstable weather