XLS or xls may refer to: .xls, the filename extension for Excel Binary File Format, a spreadsheet file format used by older versions of Microsoft Excel Blackboard Learn misuses this file extension when exporting what are actually tab-separated values files (which should have a .tsv or (less informatively) .txt extension), resulting in Microsoft Excel generating a warning message about the extension not matching the format Cadillac XLS, a prototype Cadillac concept car Exelis Inc. (NYSE symbol), a global aerospace, defense, information and services company Lusitanian language (ISO 639-3 code), an Indo-European Paleohispanic language Midwest Questar XLS, an American ultralight aircraft design Saint-Louis Airport (IATA airport code), near Saint-Louis, Senegal