1. Excel Workbook
An Excel workbook is the Excel file that holds your data and information. A workbook can contain one or more worksheets. For example, the following workbook has 3 worksheets: Sheet1, Sheet2 and Sheet3. Check How to Open a Blank Excel File.
2. Excel Worksheet
An Excel worksheet is the Tab that holds your data and information. In Excel 2016, a worksheet contains 1,048,576 rows and 16,384 columns which are 17,179,869,184 cells. For example, Sheet1 below is a worksheet. Please see next post about the Excel worksheet structure.