XLM

XLM is an abbreviation that stands for the old eXceL Macro programming language, which was the macro programming language in Excel prior to the introduction of Visual Basic for Applications in Excel 5.

XLM is entered and stored on special Macro Worksheets. It uses a superset of functions to control application and workbook state, interact with the user and read and update the contents of workbooks.  In addition to that superset of functions, XLM also uses the standard worksheet functions, and many of those have default behavious or have optional arguments still to this day, to facilitate their use in XLM.

XLM is still supported in Excel for legacy support of old workbooks which have not been updated and can still be used and authored.  Most developers have moved on to VBA or Visual Studio for Office.