A file with XLSX, XLSM, XLS, XLTX or XLTM extension is a Microsoft Excel file that uses specific standard file format. You can show or display file extension on Windows OS from Folder Options. MS Excel lets you save files in any of these file formats using the Save As option. These Excel file formats serve different purposes for working with Spreadsheet files as explained in this article.
In addition to standard file formats, Excel indirectly uses other file formats as well for a set of different operations.