A jury is required to make a unanimous or near unanimous verdict.
When the jurors, after full debate and discussion, are unable to agree on a verdict and are deadlocked with differences of opinion that appear to be irreconcilable, it is said to be a "hung jury".
The result is a mistrial.
The office of the Attorney General for California defines a hung jury as: "A hung jury occurs when jurors cannot unanimously agree on a verdict of either guilty or not guilty, followed by the judge declaring a mistrial. The case may or may not be retried, at the discretion of the prosecutor."