There are observations, so the median is the mean of the two middle numbers of the arranged set of data. Splitting the observations either side of the median gives two groups of observations. The median of the lower half of data is the lower or first quartile. The median of the upper half of data is the upper or third quartile.
The median of the lower half of data is the lower or first quartile
The median of the upper half of data is the upper or third quartile