Isn't that exactly what it says?
I borrowed the wording from Persistent Spell there, to be honest, but it really seems perfectly clear to me; I'm not sure how to expound on it. Well, OK, I guess there is one thing I could change: make it obvious that concentration isn't required to keep it running, either.
New wording has a potential problem, though: are there any spells that are just duration: concentration, with no maximum?