Relative standing

A raw number says little until you know what it is being compared with, and relative standing supplies that comparison. Percentiles give position by rank, while z-scores give position in standard deviations using $z = \frac{x - \bar{x}}{s}$, where $\bar{x}$ (x-bar) is the mean and $s$ is the standard deviation. A score of 88 on a test with mean 80 and standard deviation 4 has $z = (88 - 80)/4 = 2$, so it sits 2 standard deviations above the mean, near the 98th percentile if the scores are roughly normal. The same raw score can rank very differently in two classes whose means and spreads differ.