There are three generally used measures of central tendency:
- The mean: the "arithmetic average", sum of observations divided by count.
- The median: the central measure. The single value (or averaged pair) at the center point of an ordered listing.
- The mode: the most frequently occurring measure. Sort a set of values by frequency, and pick the most frequent instance.
Most people intend "mean" as "average", but that's not strictly the case.
https://en.wikipedia.org/wiki/Average
For our next pedant's corner post, we'll take on the distinction between descriptivist and prescriptivist definitions.
If someone says something about the "average person", they are not talking about the mean, they are talking about the median.