Starting with Microsoft Excel 2007, the default file extension for spreadsheets is .xlsx instead of the older .xls. The “x” at the end stands for “XML,” which means Extensible Markup Language – a method of encoding documents. Although you will typically not need to view the XML used to produce the spreadsheet, if you do it will appear as a series of headers, tags and data. This text then becomes the spreadsheet you see when you open Excel. Writer Bio
