A percentile is a measure of your performance relative to your peers. For example, achieving a UCAT score in the “90th percentile” means that you scored higher than 90% of candidates who sat the UCAT in the same testing season.
The highest percentile that a student can achieve is the 99th percentile (i.e. to score higher than 99% of their peers). The 50th percentile means that they achieved the median score, or a score at the middle of the data set of scores achieved by their peers, indicating that the number of candidates who scored lower than them and the number who scored higher than them is roughly equal.
To give you an idea of how UCAT scores corresponded to percentiles in 2020, here’s a compilation of the 2020 data:

(NB: The lowest possible UCAT score is 1200. The highest possible UCAT score is 3600. Approximately 14,000 students sat the UCAT ANZ exam in 2020, so 1 percentile is equivalent to around 140 candidates.)
Comparing the 2020 UCAT ANZ data with the data from 2019, it is apparent that the score required to achieve a high percentile jumped significantly in 2020. For example, to achieve a 96th percentile result, candidates needed to score 100 points more in 2020 compared to 2019:
