What is XLS?
XLS is a binary spreadsheet format developed by Microsoft for Excel. It was the standard file type before being replaced by XLSX in 2007. XLS files store data in numbered cells organized into columns and rows, supporting formulas, charts, macros, and rich text formatting. The format remains widely used for budgeting, reporting, and data analysis. Despite being a legacy format, XLS files are still compatible with modern versions of Excel, Google Sheets, Apple Numbers, and LibreOffice Calc.