| Remission | A period of time with minimal or no depressive symptoms. Remission ends with either relapse or recovery. |
| Relapse | Reemergence of the index depressive episode. Relapse occurs during remission, prior to onset of recovery. |
| Recovery | Recovery occurs when patients remain well for a period of time exceeding the interval that defines remission. Recovery can be indefinite or can end with recurrence. |
| Recurrence | Recurrence represents the appearance of a new episode of major depression. Recurrence is distinguished from relapse, which represents the return of the index episode. |
| Continuation treatment | Continuation treatment occurs after acute treatment and serves to preserve and enhance remission and prevent relapse of the index episode. Continuation treatment ends with relapse (in which case acute treatment resumes), or leads to maintenance treatment. |
| Maintenance treatment | Maintenance treatment follows continuation treatment and represents ongoing treatment after patients achieve recovery. Maintenance treatment serves to prevent recurrence of new depressive episodes. |
