Scope determines the level at which the filter shouild be applied.
you have Region, country, State and Revenue data items in your report.
Region, Country and State were grouped.
If you Total the Revenue field you will get footers(sub totals) for Country and Region.
Now if you want to filter Country which has > 50000 revenue, then create a summary filter like Total(Revenue) > 50000 and set the scope to Country.