Besides workbooks, in Excel, it is also possible to rename individual worksheets if you want to organize your data more efficiently:
Worksheet: You can rename a specific sheet by either double-clicking the sheet tab at the bottom of your window or right-clicking on it and choosing "Rename".
Workbook: Workbook is another term used for the whole Excel file. To rename a workbook you can perform a "Save As" while the file is open or directly rename the file via your computer's file explorer.