What is Open Verdict?

Legal Definition
The open verdict is an option open to a coroner's jury at an inquest in the legal system of England and Wales. The verdict means the jury confirms the death is suspicious, but is unable to reach any other verdicts open to them. Mortality studies consider it likely that the majority of open verdicts are recorded in cases of suicide where the intent of the deceased could not be proved, although the verdict is recorded in many other circumstances.
-- Wikipedia
Legal Definition
A verdict of a coroner's jury which finds that the subject "came to his death by means to the jury unknown," or "came to his death at the hands of a person or persons to the jury unknown." that is, one which leaves open either the question whether any crime was committed or the identity of the criminal.
-- Black's Law Dictionary