Handbook of Descriptive Statistics/Measures of Central Tendency/Trimean
The trimean is a resistant measure of central tendency.
Instead of focusing on the median, the trimean is calculated by adding twice the sum of the median to the sum of the 25th percentile and 75th percentile and then divide the sum by four.
(25%ile + 2* 50%ile + 75%ile) / 4 = Trimean
John Tukey came up with this in a 1982 publication. This is part of the family of L-Estimates which are statistics based on linear combination of the order statistics.
Because it depends on order statistics it is a robust measure, but by including the 25%ile and 75%ile this lowers the breakdown value of the measure.