"What are Percentile Rankings?
Each of your five GMAT scores includes a percentile ranking, which indicates the percent of test takers that you performed better than. For example, a ranking of 75% means that 25% of test takers performed as well or better than you, and 75% did not do as well. While your scores will not change over time, your percentile ranking may because rankings are recalculated every year using exam data from the prior three years."
-https://www.mba.com/exams/gmat-exam/scores/understanding-your-score