Imagine opening an Excel file expecting to see numbers, only to find that every cell displays formulas like =SUM(A1:A10), instead of the actual results. It can be confusing and frustrating, especially ...
That indicates a SUM formula (adding things up) for all the sheets that are titled Y1 to Y10 (so 10 years' worth), and looking at cell B3 in each. The result will be the sum of all 10 years.