The XLSX file format is the default spreadsheet format used by Microsoft Excel, starting with Excel 2007. It's based on the Open XML standard, which uses a combination of XML and ZIP compression to store spreadsheet data. This format allows for efficient storage of large amounts of data, formulas, charts, and other spreadsheet elements. XLSX files can contain multiple worksheets, each organized into rows and columns of cells. These cells can hold various types of data, including numbers, text, dates, and formulas. The format also supports rich formatting options, such as fonts, colors, borders, and cell styles. Because it's an open standard, XLSX files are widely supported by other spreadsheet applications, making it a versatile format for data exchange and collaboration. The use of XML allows for easier parsing and manipulation of the data programmatically, making it suitable for automated data processing and reporting. Furthermore, the ZIP compression reduces file size, making it easier to share and store large spreadsheets. The XLSX format is a significant improvement over the older XLS format, offering better data integrity, security, and interoperability.