World Health Organization – 1992
This arises as a delayed and/or protracted response to a stressful event or situation (either short- or long- lasting) of an exceptionally threatening or catastrophic nature, which is likely to cause pervasive distress in almost anyone (e.g. natural or man-made disaster, combat, serious accident, witnessing the violent death of others, or being the victim of torture, terrorism, rape, or other crime).