Command Line
Right-clicking in the Command line produces a shortcut menu with access to the six most recently used commands, as well as other options.

Status Line
Right-click on any of the buttons in the status line to display a menu to toggle on and off the setting and provide access to the dialog box controlling the setting.

Dialog Boxes
Right-clicking in most dialog boxes offers options like rename, delete, cut, copy, and paste.  Other context-sensitive  selections may be present.

Toolbars
Right-click on a toollbar to quickly turn on and off a toolbar.  Right-click in the empty space next to a toolbar to display a list of menu groups.

Tabs
Right-click on a layout tab to display plotting, page setup, and various layout options.

Using Right-click
The use of shortcut menus is controlled in the Options dialog box.  On the User Preferences tab, select the Right-click Customization button.