iOS Question:

In iOS 4.0 to iOS 6.x, double-clicking the home button activates the application switcher. A scrollable dock-like interface appears from the bottom, moving the contents of the screen up. Choosing an icon switches to an application. To the far left are icons which function as music controls, a rotation lock, and on iOS 4.2 and above, a volume controller. Holding the icons briefly makes them "jiggle" (similarly to the homescreen) and allows the user to force quit the applications by simply tapping the red minus circle that appears at the corner of the app's icon.