It stands for “Comma-Separated Values”. A .csv file doesn’t have any formatting (i.e., colors, font, column-width) and can only be one sheet in a workbook. When you save a Microsoft Excel Workbook to a .csv format, you will usually get a warning that you can’t save multiple sheets in .csv format. That's ok. The point of saving to a .csv file is that you are removing extra sheets and formatting from the workbook.