Object Format

Hi, I use C # to create/open file.

Excel.Application xlApp;
            Excel.Workbook xlWorkBook;
            Excel.Worksheet xlWorkSheet;
            Excel.Range range;

            openFileDialog1.Filter = "(*.xls)|*.xls|(*.xlsx)|*.xlsx";
            openFileDialog1.Title = "Select an excel file";
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
                fname = openFileDialog1.FileName;
            xlApp = new Excel.ApplicationClass();
            xlWorkBook = xlApp.Workbooks.Open(fname, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);
            xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);

5 in this statement is Object foramt,

xlWorkBook = xlApp.Workbooks.Open(fname, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "\t", false, false, 0, true, 1, 0);

but what is meant by 5?