In Short

YouTube is Google's online video service. With it you can upload your own videos or watch any of the millions and millions of videos — from cats on pianos to the latest Hollywood trailers and to independent movies and TV shows — uploaded by people around the world. While you can view YouTube in the built-in Safari web browser, Google also offers dedicated YouTube apps for both iPhone and iPad that provide extra features and functionality.

YouTube was one of the default apps on the iPhone and iPad up until iOS 6 but when Apple and Google couldn't come to terms over advertising — Apple didn't want it in the built-in app — they parted ways and YouTube went to the App Store. (YouTube remains a default app on the Apple TV, however.)