Which of the following is a biased estimator? That is, which of the following does not target the population parameter?

Choose the correct answer below.
Variance
Mean
Median
Proportion

Step 1 ：Understand what a biased estimator is. A biased estimator is an estimator that does not target the population parameter. It does not accurately represent the population parameter it is supposed to estimate.

Step 2 ：The variance, mean, and proportion are all unbiased estimators because they accurately represent the population parameters they are supposed to estimate.

Step 3 ：The median, however, can be a biased estimator because it does not always accurately represent the population parameter it is supposed to estimate.

Step 4 ：Therefore, the answer to this question is the median.

Step 5 ：Final Answer: \(\boxed{\text{Median}}\)