It is called screen pinning. Screen pinning allows you to pin a specific app to your phone screen so that whoever is using your phone can only use that app and cannot navigate throughout your phone. If they find out how to unpin the app, they will be greeted with your lockscreen provided your device is secured with some form of security. This means that when you hand your phone off to your suspicious sibling to make a brief call or play a game, they will not exit the app and somehow find there way to your Whatsapp or Facebook app and see all the stuff you do there.

See how to do it. Check under Android @ www.itechdis.com