Files with the .XLSM extension are spreadsheets with active macro functions, namely pages of rows and cells in a table distribution containing data, formulae, graphs, and assigned formatting, as well as macros constructed using the VBA language – short for Visual Basic for Applications. Files of this type are typical for Microsoft Excel.

Data in XLSM files is saved in the Open XML format, and is different from XLSX files only in that it contains active macro functionality. This way, MS Excel prevents the automatic triggering of macros in files that do not have the said extension, even if they do, in fact, contain macros.