Depression was a mental condition characterized by feelings of sadness for no reason, little interest in participating in activities, or interacting with other people. It could be caused by a range of factors, such as grief, events in one's life, drugs, other medical and psychological conditions, or a nervous breakdown.
Assistance from others or drugs could help, but not totally remove the condition.
A related condition was chronic depression, in the symptoms of depression remained for long periods of time.
Chronic depression was one of a number of handicaps that randomly afflicted Grey Orions, due to their genetic mutilation. Affected Grey Orions suffered bouts of extreme depression that lasted days. (FASA RPG - The Orions module: Book of Deep Knowledge)