这一句话什么意思?

Private Sub Command1_Click()
Common.DefaultExt = "*.mdb"
Common.Filter = "*.mdb"
Common.ShowOpen
Text1.Text = Common.FileName
cn.Open "Provider =Microsoft.Jet.OLEDB.4.0;Data Source=" & Common.FileName & ";Persist Security Info= False"
Set rs = cn.OpenSchema(adSchemaTables)
Do Until rs.EOF
If Left(rs!TABLE_NAME, 4) <> "MSys" Then

List1.AddItem rs!TABLE_NAME
End If
rs.MoveNext
Loop
rs.Close
End Sub
If Left(rs!TABLE_NAME, 4) <> "MSys" Then
尤其是MSYS J是什么?