Alt-Tab

Alt+Tab ↹ is the common name for a keyboard shortcut that has been in Microsoft Windows since Windows 3.0. This shortcut switches between top-level windows without using the mouse; hence it was named Task Switcher. Perhaps the most common use of Alt+Tab ↹ is to alternate between the two most recent tasks, but it can also be used to switch to any running program that has a top-level window.