It is the way you would like the date displayed when you view it. Here are some options:
01/12/2010
Decenber 13, 2009
1-Mar-54
MS Excel 2003 and earlier use the XLS format. MS Excel 2007 and later use the XLSX format.
Default file format for Excel 2003: .xls Default file format for Excel 2007: .xlsx Note: You can't open lower version file format in upper version. If you want to do this then you will have to download the compatibility pack.
..xlsx is a Excel 2007 format, whereas .xls is Excel 2003 or earlier. Excel 2007 allows you to save in multiple 2007 formats: ..xlsx - Normal Excel 2007 format ..xlsm - Macro-Enabled format ..xlsb - Binary format Save your files as 2003 under Save as Type and you should be fine.
Format / Cells / Date
Excel 2003 and earlier: .XLS Excel 2007 and later: .XLSX
If you do not like how the dates are formatted, then change the date format of the cell to whatever style you would like to display.
The cell has been formatted to be in date format. You just need to format the cell to show numbers. If a number is formatted as a date, it will show an actual date.
To indicate that the basic file format is XML in Excel 2007 and later.
In Excel 2007, use the "Format as Table" button in the Styles section of the Home tab.
.xlsx is the file format used in Microsoft Office Excel 2007. It is NOT backwards compatible (i.e. Excel 2003 and earlier versions cannot open it). The file is XML based and smaller in size than the .xls format. It is possible to open, edit, and save a .xls file in Excel 2007 for backward compatibility.
The formula is =NOW(). Ensure you format the cell to display the date format you want.
.xlsx is the file format used in Microsoft Office Excel 2007. It is NOT backwards compatible (i.e. Excel 2003 and earlier versions cannot open it). The file is XML based and smaller in size than the .xls format. It is possible to open, edit, and save a .xls file in Excel 2007 for backward compatibility.