Complex sentence: Alt-Tab is the common name for a complex keyboard shortcut on Microsoft Windows 3.1 onwards used for switching between top-level windows without using the mouse; hence it was named "Task Switcher" ("Flip" in Windows Vista).
Split into simpler sentences: Alt-Tab is the common name for a complex keyboard shortcut on Microsoft Windows 3.1 onwards used for switching between top-level windows without using the mouse. Hence the name "Task Switcher" ("Flip" in Windows Vista).