The mode is also a measure of average (central tendency), but again, different from how you have likely thought of an average before.
The mode is simply the value in a data set that is represented the most times.
Again, let's refer to my ongoing test grade example:
The grades received for a test in a math class, composed of 13 students, were:
65, 98, 92, 43, 76, 64, 69, 72, 75, 85, 96, 90, 90
When you rearrange them from lowest to highest, you can quickly identify which value appears the most times:
43, 64, 65, 69, 72, 75, 76, 85, 90, 90, 92, 96, 98
So, for this data set of math scores, the mode was 90... that is, more students scored 90 than any other single grade achieved.
Hopefully this series of posts has helped to explain the calculation of median, mean, and mode. As you will see in your studies, each has its own applications and are useful in their own ways. It is important to realize though that they are all related as forms of average, and they all describe the centeredness of a data set. See my post here for tips on how to choose which of these measures of central tendency to use.
As always, leave a comment if you need clarification or more information on the topics I've posted. As well, as I have done with this series of posts, I will try to address any requests students may have as well in future posts. :)