The word "median" has several different meanings in mathematics all related to the "middle" of mathematical objects.
The statistical median is an order statistic that gives the "middle" value 
of a sample. More specifically,
it is the value 
such that an equal number of samples are less than and greater than the value (for
an odd sample size), or the average of the two central values (for an even sample
size). The Wolfram Language function
Median[list]
can be used to find the statistical median of the elements in a list.
A triangle median is the Cevian from one of its vertices to the midpoint of the opposite side. The medians intersect in a point known as the triangle centroid that is sometimes also called the median point.
Similarly, a tetrahedron median is a line joining a vertex of a tetrahedron to the geometric centroid of the opposite face.
The median of a trapezoid is the line segment determined by the midpoints of the two nonparallel sides.
