With the introduction of iOS 4, multitasking capabilities were also introduced. On iOS 3 and earlier, leaving an app by pressing the home button would close it. But on iOS 4 and later, when you are in an app and then press the home button, this does not actually close the app. The state of the app is just suspended, ready to resume when you re-open it. If the app is compatible with multitasking, it may continue running even after exited by pressing the home button. This article will walk you through how to completely close an app.
How to Entirely Close Apps