“The average is calculated by adding up all of the individual values and dividing this total by the number of observations. The median is calculated by taking the “middle” value, the value for which half of the observations are larger and half are smaller.”

So for example, in a country with 99% poor people, and 1% insanely rich people, the median person’s wealth is actually really small (like the poor people), but the average person’s wealth is kinda big (except a person with that mid-ground wealth doesn’t actually exist in the country).

In the case of voters, this means that in a country of highly polarized views and power, so of imbalanced sides, the median and average voter can be very different. One is what the people want, the other is what the power wants.

"The median voter theorem is a proposition relating to ranked preference voting put forward by Duncan Black in 1948.[1] It states that if voters and policies are distributed along a one-dimensional spectrum, with voters ranking alternatives in order of proximity, then any voting method which satisfies the Condorcet criterion will elect the candidate closest to the median voter. In particular, a majority vote between two options will do so. A loosely related assertion had been made earlier (in 1929) by Harold Hotelling.[3] It is not a true theorem and is more properly known as the median voter theory or median voter model. It says that in a representative democracy, politicians will converge to the viewpoint of the median voter.[4] "

Emphasis mine.