In statistics there are many useful indices that we can use to describe data. Some common terms are median, mode and mean.

Median is the middle value found in a list of data which is arranged in ascending order (e.g., the median of {1, 2, 3, 4, 5} is 3). If the data contains even number of observations, then we take the mean of the two middle values as median (e.g., the median of {1, 2, 3, 4, 5, 6} is 3.5).