The Actual check box on the AP Vendor Merge form.

Select this check box to designate this vendor as a 'parent' vendor; that is, the vendor to which selected duplicate vendors will be merged. You can only select one vendor as Actual per merge session.
Note: Vendors with this check box selected will continue to display in the grid when performing subsequent vendor merges if they meet the filter criteria. Only vendors flagged as unique or duplicates are removed from the grid.

Leave this check box unselected if this vendor should be designated as a duplicate vendor or a unique vendor. You can also leave this check box unselected if you are not sure whether this vendor is an actual, duplicate, or unique vendor.