noun

1. In psychotherapy and psychiatry, a state of mind producing serious, long-term lowering of enjoyment of life or inability to visualize a happy future.

   “I used to suffer from depression, but now I'm mostly content with my life.”

2. An area that is lower in topography than its surroundings.

3. In psychotherapy and psychiatry, a period of unhappiness or low morale which lasts longer than several weeks and may include ideation of self-inflicted injury or suicide.