AVERAGE, AVERAGEA, AVERAGEX – DAX Guide

AVERAGE: Returns the average (arithmetic mean) of all the numbers in a column.
https://dax.guide/average/

AVERAGEA: Returns the average (arithmetic mean) of the values in a column.
https://dax.guide/averagea/

AVERAGEX: Calculates the average (arithmetic mean) of a set of expressions evaluated over a table.
https://dax.guide/averagex/