An XLS file is a spreadsheet file created by Microsoft Excel, the most widely-used spreadsheet program. It stores data in worksheets, charts, and macros. XLS files are saved in the Excel Binary File Format, which was the primary format until the Office Open XML format (.XLSX file extension) replaced it in Excel 2007.
An XLS spreadsheet is used for organizing, analyzing, manipulating, and visualizing data. The spreadsheet commonly consists of a table with rows and columns. The table cells in the file may contain manually entered data or the results computed from the data of other cells.
NOTE: Although Excel users primarily save their spreadsheets in the Office Open XML format (XLSX files), Excel still supports the XLS format.