Explanation

The keyboard shortcut to minimize an Excel worksheet is Ctrl+F9.

This shortcut also restores all workbook windows that are maximized. 

Here are some other Excel keyboard shortcuts:

Ctrl+F10: Maximizes or restores the selected workbook window

Ctrl+F7: Moves workbook windows that are not maximized

Ctrl+F8: Performs the size command for workbook windows that are not maximized

Ctrl+P: Opens the print dialog box

Ctrl+Z: Undoes the last action

Alt+Space: Displays the Control menu for the Main Excel window

Alt+F4: Closes Excel

F6/Shift+F6: Moves to the next or previous pane in a workbook that has been split

Ctrl+Tab/Ctrl+Shift +Tab: Moves to the next or previous workbook window