I'd say the target is getting the ball between the posts, under the crossbar, and over the goal line, as that's what gives a goal.miss.
I'd say that the target is to score a goal, that is to hit the goal without it hitting the keeper so that it won't go in.
In a similar case to it being off target to hit the woodwork, you can argue that it is off target to when the ball hits the keeper. And in the definition it clearly isn't. Therefore you could argue that hitting the post also is hitting the target, as its actually closer to hitting the target than when hitting the keeper.