\begin{definition}[Definition:Percentile]
Let $D$ be a finite collection of data regarding some quantitative variable.
Let $D$ be divided into precisely $100$ classes.
A $P$th '''percentile''' is a value in the interval defined by the $P$th class such that:
:$\dfrac P {100}$ of the data in $D$ fall at or below the value chosen
:$1 - \dfrac P {100}$ of the data in $D$ fall at or above the value chosen.
Arbitrarily more precise definitions may be contrived as necessary to define a unique percentile for a given study.
\end{definition}