XLSX

Office Open XML Spreadsheet (.XLSX) is the default file format for documents used by Microsoft Excel as of Excel 2007. In prior versions, the default version was XLS.

History
This (along with the other Office Open XML items DOCX and PPTX) was initially standardized as ECMA-376 in 2006. Three formats of this standard have been produced; the second version also corresponds to ISO/IEC 29500.