Median

Central tendency measure that minimizes the sum of the L1 norm between it and all the other points.

$$\text{Med}(X)=\{\begin{array}{ll}X\left[\frac{n+1}{2}\right],& n\text{ is odd}\\ \text{mean}\left(X\left[\frac{n}{2}\right],X\left[\frac{n+1}{2}\right]\right),& n\text{ is even}\end{array}$$

• The middle value of an odd-length list or the average of the two middle values of an even-length list
• $X$ is an ordered list