中位数（又称中值，英语：Median），统计学中的专有名词，代表一个样本、种群或概率分布中的一个数值，其可将数值集合划分为相等的上下两部分。对于有限的数集，可以通过把所有观察值高低排序后找出正中间的一个作为中位数。如果观察值有偶数个，则中位数不唯一，通常取最中间的两个数值的平均数作为中位数。

一个数集中最多有一半的数值小于中位数，也最多有一半的数值大于中位数。如果大于和小于中位数的数值个数均少于一半，那么数集中必有若干值等同于中位数。

设连续随机变量X的分布函数为F(X)，那幺满足条件P(X≤m)=F(m)=1/2的数称为X或分布F的中位数。

In statistics and probability theory, a median is the number separating the higher half of a data sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to highest value and picking the middle one (e.g., the median of {3, 3, 5, 9, 11} is 5). If there is an even number of observations, then there is no single middle value; the median is then usually defined to be the mean of the two middle values (the median of {3, 5, 7, 9} is (5 + 7) / 2 = 6), which corresponds to interpreting the median as the fully trimmed mid-range. The median is of central importance in robust statistics, as it is the most resistant statistic, having a breakdown point of 50%: so long as no more than half the data are contaminated, the median will not give an arbitrarily large result. A median is only defined on ordered one-dimensional data, and is independent of any distance metric. A geometric median, on the other hand, is defined in any number of dimensions.