As I said, it doesn't mean anything
But the fact that his magic can put out that amount of energy IS impressive. Could it stop a bullet? In reality, nobody can say for sure. But there is a hell of a lot of evidence that points towards it.
Yes, there are unblockable/undodgeable spells. Accio, Langlock, or Levicorpus.
Obviously you can't dodge Accio. I mean, it's a summoning spell. Harry manages to summon his Firebolt by waving his wand vaguely in the direction of the castle; clearly you don't need to be accurate at all to get a successful Accio.
Langlock is another, though that's not really useful.
Impedimenta technically falls under this category, because it can and has been shown to extend to your entire field of vision.
Sectumsepra and Dolohov's slash both cover your entire field of vision.
The most useful, however, is Levicorpus. Why? Because Harry just has to think (as demonstrated by Severus not flicking Harry's wand upwards as he did before) and the victim goes bottoms up (also by him simply levitating the nearest target, Ron, despite not being facing him or pointing at him or anything).