The document discusses the median, including its definition, calculation, merits, and demerits. The median is the middle value of a data set arranged in order. It is calculated by arranging the values from lowest to highest and selecting the middle one. Merits of the median include that it is simple to calculate, unaffected by outliers, and represents typical values. Demerits include that it lacks representativeness for widely dispersed data, is erratic for small data sets, and cannot undergo algebraic treatment. The document also provides formulas for calculating the median of individual series, discrete series, and continuous series.