zlacker

It means 83% of reviewers gave it a 'passing grade' which is defined as a 6/10+.

The formulation is a way to collapse precise scores into a binary classification of thumbsup or thumbsdown. So, another way to put it would be 83% of reviewers 'liked it'

Side note, I used to really like Rotten Tomatoes 10+ years ago but I noticed a drop in quality, likely Goodhart's law in action as some other commenters here have pointed out.