The average of two number is their mean...................A1C...............if 1 is a letter........it would be A............what is the mean of A and C in our alphabet..............B for Batman, silly..........

www.merriam-webster.com/dictionary/average

Merriam‑Webster

Simple Definition of average. : a number that is calculated by adding quantities together and then dividing the total by the number of quantities. : a level that is typical of a group, class, or series : a middle point between extremes.