Alt-Tab is a powerful keyboard shortcut in the Windows operating system that allows users to quickly switch between open applications or windows. It plays a crucial role in multitasking and productivity, enabling users to seamlessly transition between different tasks without the need for a mouse or excessive clicking.

In the Windows environment, Alt-Tab is a default feature that has been present since the early versions of the operating system. It has become an integral part of the user experience, providing a convenient way to navigate through multiple applications or documents simultaneously.

Examples:
1. Switching between Applications: Pressing Alt-Tab once will bring up a small window displaying thumbnail previews of all open applications. By continuing to hold down the Alt key and pressing Tab, users can cycle through the list and release the keys to switch to the desired application.

2. Switching between Windows of the Same Application: When multiple windows of the same application are open, holding down the Alt key and pressing the Tab key will display a thumbnail preview of each individual window. Releasing the keys will switch to the selected window.

3. Using Alt-Tab with Other Modifier Keys: By combining Alt-Tab with other modifier keys, additional functionality can be achieved. For example, using Alt-Shift-Tab instead of Alt-Tab will cycle through the list of open applications in reverse order.

4. Customizing Alt-Tab Behavior: Windows provides options to customize the Alt-Tab behavior. Users can access these options by going to "Settings" > "System" > "Multitasking" and selecting their preferred settings. For example, users can choose to display only the active desktop windows or disable the thumbnail previews altogether.