Quartile

Quartiles split ordered data into four parts, marked by the first quartile $Q_1$, the median, and the third quartile $Q_3$. The first quartile is the median of the lower half and the third quartile is the median of the upper half. For example, in 2, 4, 6, 8, 10 the median is 6, so you exclude it and get $Q_1 = 3$ and $Q_3 = 9$. This site uses the median-excluded convention (the TI-84 method), which drops the overall median when the count is odd.