The "Alt Key" is a modifier key found on computer keyboards, typically located next to the spacebar. It is used in combination with other keys to perform special functions or shortcuts. For example, pressing the Alt Key along with the F4 key can close an open window in many operating systems. In addition to its primary function, the Alt Key can also be used to access menu options in software applications. By holding down the Alt Key and pressing a letter, users can quickly navigate through menus, enhancing productivity and efficiency while using their computers.