Median:

               1. The number in the middle of an ordered list of numbers: median

                e.g.  1, 2, 4, 4, 4, 5, 5, 6,7          There are 9 numbers and 4 is the median
 
            2. When the list is even, the median is the average of the two middle numbers
 
                e.g.  1, 2, 4, 5, 5, 6          both 4 and 5 middle numbers so median = (4+5)/2 = 4.5