What does “query to referee” in the tracking system of Physical Review Letters imply? After the report was sent in, the status of my manuscript in the tracking system of Physical Review Letters indicated a query to referee.
What does this mean?

The editor explained further information is needed from the referee.
This is basically what query to referee means.
But I am wondering what it implies. Is the report good or bad?
Does anyone has any experience on this issue, and what is the outcome?
It can mean that there was something problematic about the referee's report.  This can indicate that there is some kind of inconsistency between what the referee says in different parts of the report.  For example, the referee may have provided a very positive written evaluation, but accidentally clicked the box saying "Reject."  If that happens, the editor will naturally ask the referee to clarify what they actually meant.

One other thing it can mean, particularly in connection with a journal like Physical Review Letters, which has selection criteria that require more than just a correct and interesting paper.  If a paper is deemed to be, in fact, correct and interesting, there may still be some additional back-and-forth communication between the editor and referee(s) to ascertain whether the work is important enough for that particular journal.