On the iPad, apps remain in memory when an app is not visible. In some cases you'll need to kill the app to erase the memory from the tablet.
Killing the app can be done by double tapping the home button (button on the front frame of the iPad).
Double-tapping the home button will show the active applications as smaller screens (see image).
Swipe the application 'up', out of the tablet screen to close it (you can also close 2 or even 3 apps at the same time).
To finish, press the home button again you will now go to your home screen.