Originally Posted by buffs79
Well, an alternate universe is a completely seperate universe from all other Trek mythos (such as the Mirror Universe, & maybe the Yest. Enterprise universe)
While an Alternate Timeline was faithful to the "Main" timeline up to a certain point, where it was changed.
This film has a timeline that is completely normal up to when the Narada attacks the USS Kelvin. The moment that happens we have an alternate timeline.
Not so sure about the last part, I think there's something a little more to it than that.