What's this sentence use: " sFil = Dir"?

The sentence

sFil = Dir

at the end of the code below, what is its role?

Sub test()


Dim sPath As String
Dim sFil As String
Dim FolderPath As String
   Dim diaFolder As FileDialog

 
   Set diaFolder = Application.FileDialog(msoFileDialogFolderPicker)
    diaFolder.AllowMultiSelect = False
    diaFolder.Show
    FolderPath = diaFolder.SelectedItems(1)

 

sPath = FolderPath & "\" 'location of files
'MsgBox "FolderPath: " & FolderPath & ";" & "sPath: " & sPath

sFil = Dir(sPath & "*.xls")

Do While sFil <> ""


 Set oWbk = Workbooks.Open(sPath & "\" & sFil, 0)



oWbk.Close
sFil = Dir

Loop

End Sub

Thanks!!