What does "awaiting reviewer reply" mean? What does "awaiting reviewer reply" mean? Is it same as "under review" and "awaiting reviewer scores"?"
It means reviewers have been invited but have not responded to the invitation.

It's not necessarily the same as 'under review' and 'awaiting reviewer scores'. The latter is a clear term that means reviewers have agreed to review the article, but have not provided a report yet. The former is a vague term that could mean anything: reviewer has been invited, reviewer has agreed to review, maybe even reviewer has submitted a review but there're other reviewers who have not yet completed their reviews.

In any case, there's nothing to do except wait.