ActiveSheet.UsedRange.Columns.Count - 8 what does it mean?

Question

what does ActiveSheet.UsedRange.Columns.Count - 8 mean in vba?

How does vba know the usedRange?

Answer 1

I think if you try:

Sub Macro3()
a = ActiveSheet.UsedRange.Columns.Count - 3
End Sub  

with a watch on a you will see it does make a difference.