Genuinely have no idea mate, not sure if there is an official definition either. But for me if the ball is crossed and is not cleared and it results in another or other attempts on goal I'd still call it the result of the corner/cross, ball is still in play and still active.
An extreme example would be this cross (you have to assume that the cross was a dead ball of course) in the Accrington Stanley vs Crawley Town game from the weekend. I'd say this is all part of a single piece of play and as a result of the cross, ball not cleared. You say wee tomato and I say tomato.