The CSV ("Comma Separated Values") file format is often used to exchange data between differently similar applications. The CSV file format is useable by KSpread, OpenOffice Calc and Microsoft Excel spread-sheet applications. Many other applications support CSV in some fashion, to import or export data.
A .CSV file is very similar to a XML/OOXML file type in Excel. In a CSV file the data is structured very tabular and has compatibility with programs like Microsoft Excel, Open Office Calc, or Google Spreadsheets.
For information on how to convert any Excel file into .CSV format, please click here.