Watch TV programs movies or videos. Yes you can watch any movie you have downloaded to your iPad from iTunes or other services on your iPad without a WiFi connection. I am a frequent flyer and had several frustrating occasions where I was not able to watch a rented movie on my iPad without WiFi connection on the plane.
In iTunes click on your iPad from the Device menu. Moreover it is all for free as part of the standard account. After you start watching the movie you have 48 hours to finish it. As long as it is fully downloads you can watch it without wifi.