n-th percentile represents the value below which
n% records can be found. It's calculated by sorting a data set and dividing it into 100 equal groups, and then dividing the same data set into two parts where the lower part contains
n% of the data, and the higher part contains the rest.
50th percentile of a data set is equal to its Median.
For example, if we talk about Measuring Request Latency, 95th percentile is the time in which 95% of all the requests will be completed.
Looking at the 99th percentile will give us a time in which all of our requests would be completed, excluding the slowest 1%.