Depression is a western psychology condition that has quite a few types and the they vary according to which classification system you're using. The list below from Wikipedia is a good representative. The symptoms from all types of depression are found in many Oriental Medicine disharmonies.
Psychotic major depression (PMD),
Seasonal affective disorder (SAD)
Recurrent brief depression
Minor depressive disorder
Depressive Disorder Not Otherwise Specified
The most common are excesses or deficiencies of Yin or Yang of the Heart, Liver, or Kidney although it is not uncommon for other organs to be involved. The most easily recognized type of depression - tiredness, no desire to do anything, brooding, worrying, difficulty going to sleep, poor appetite, distractedness, mental restlessness - is a result of of Qi & Yang deficiency of one or all of the Kidney, Heart, Spleen. Treatment includes stregthening of specific aspects of these organs and this isusually done by use of acupuncture, herbal medicnes and tuina.
[link to Dis EW dep]