What is an outlier in a data set and how can it affect the mean and median of the data set?

An outlier in a data set is a value that significantly differs from other data points. When calculating the mean, outliers can skew the result, pulling it towards the outlier's value. On the other hand, outliers have minimal effect on the median since it is not influenced by extreme values. Therefore, it's important to identify and handle outliers carefully to accurately represent the central tendency of the data.