old YouTube app
iPhone 4S, iOS 5.1.1, application
If you mean the one at the bottom of that screen that looks like an old TV screen then that's the built-in YouTube app (it's part of IOS), it can't be deleted (though you can hide it via Settings > General > Restrictions)
Thany you very much on the new iOS will they be replacing it do you know?
Reports are that iOS 6 will not include a YouTube app and that Google will be providing one of their own, but that has not yet been confirmed.
Regards.
old YouTube app