Median
The median is the middle value in a set of data when the numbers are arranged in order of size (either ascending or descending). If there is an even number of values, the median is the mean of the two middle numbers.
Example
In the ordered set $3, 5, 7, 9, 11$, the median is $7$. In the set $2, 4, 6, 8$, the median is $\frac{4 + 6}{2} = 5$.