Though most grief is a mild sort of injury compared to how bad such injuries can get, some griefs are experienced as more traumatic, and can become difficult to resolve. The term "Pathological Grief" is sometimes applied to people who are unable to work through their grief despite the passage of time. It can take most people up to several years to get past a serious loss. A pathological grief reaction may be diagnosed after a long time (one or more years) have passed and the grieving person is not improving. By labeling someone's grief as pathological, a doctor is indicating that the grieving process resolution is delayed for some reason and that professional help is needed. No disrespect is intended toward the patient in using this term.
There is no absolute time frame within which grief is considered pathological, although there are cultural norms that serve as guidelines. In North America a person might be judged as being "stuck" if they are still actively grieving 18 to 24 months after their loss. An unremitting 'overly intense' grief process of shorter duration might also be labeled as pathological. Keeping these guidelines in mind, know that it is very much appropriate to encourage people who appear to be stuck in their grief process to seek professional grief counseling.