AVG - similar to SUM calculates over the entire measure
WINDOW_AVG - is a table calc that averages over the data in the window only, or a subset of that if required.
can you give example
Main deference between Avg and Window Avg is
Avg calculate like sum(sales)/Count (lowest granularity )
see the below example , I am taking the report at category level , but it takes @ count of product Name count.
window Avg like Total Sales/ count of rows
in this case it takes report level avg.