A decision has not yet been made towards a particular subject. Its meaning comes from the fact that when a jury is 'still out', it is still deliberating over a verdict. It is also commonly used to express a general sense of ignorance or uncertainty applied to a group; saying "The jury is still out on X" can be the same as saying "X is anyone's best guess". This lack of certainty is not confined to the individual, but is shared by the group that is assumed from context.
Part of the American Idioms project