What does "Awaiting Reviewer Scores" mean within the context of a ScholarOne submission system?
With a typical ScholarOne configuration, "Awaiting Reviewer Scores" means that it is actually out with (at least some) reviewers, while "Under Review" would instead mean the previous stage, where it is being considered by the handling editor(s) and might still be rejected without review.

After the review scores come back, a manuscript then returns to the handling editor for a recommendation, and thence up to the chief editor(s) for a decision.