Final answer:
The common keyboard shortcut for the 'Alt' key is '[Alt]'. It is often used in combination with other keys, like [Tab] to switch apps and [F4] to close windows.
Step-by-step explanation:
The keyboard shortcut that is commonly used for the "Alt" key is [Alt] itself. When instructions or documentation refer to keyboard shortcuts that involve the "Alt" key, they will indicate this with '[Alt]' followed by another key or keys. For example, [Alt] + [Tab] is a common shortcut used to switch between open applications on a Windows computer, and [Alt] + [F4] is used to close the current window or program.