Definition:
.xls is a file extension used on computers running Microsoft Windows to identify files created in Microsoft Excel.
A file extension is the group of letters that appear after the last period in a file name. File extensions are usually 2 to 4 characters long.
.xls was the default file extension for versions of Excel up to Excel 2003.
Excel 2007 has a different default file extension but it can save files in the .xls format in order to make them compatible with earlier versions of Excel.
For most users, the main benefit of the file extension is that it allows them to double click on .xls files and they will open in Excel.
File extensions can also make it easier to identify files when viewing them in My Documents or Windows Explorer
.