The "Median of Medians" is an algorithm used to find an approximate median in a list of numbers. It works by dividing the list into smaller groups, typically of five elements each, and calculating the median of each group. These medians are then collected to form a new list, from which the median is again calculated. This process helps in efficiently narrowing down the search for the overall median. This method is particularly useful in selection algorithms, such as the Quickselect algorithm, where finding the median can improve performance. By using the "Median of Medians," one can achieve a more balanced partitioning of data, leading to better average-case time complexity.