Mean
The average value, calculated by adding all the observations and dividing by the number of observations.

Median
Middle value of a list. If you have numbers 2, 3, 4, 5, 6, 7, and 8, the median is 5. Medians are often used when data are skewed, meaning that the distribution is uneven. In that case, a few very high numbers could, for instance, change the mean, but they would not change the median.

Other definitions include the smallest number such that at least half the numbers in the list are no greater than it. If the list has an odd number of entries, the median is the middle entry in the list after sorting the list into increasing order. If the list has an even number of entries, the median is equal to the sum of the two middle (after sorting) numbers divided by two. The median can be estimated from a histogram by finding the smallest number such that the area under the histogram to the left of that number is 50%. But all mean the same thing in the end.

Mode
For lists, the mode is the most common (frequent) value.

Bandolier. EBM glossary. Internet. Accessed on July 3, 2016.