One of Apollo's many epithets, bestowed upon him by the Spartans way back when. But why Carneus, you ask? Let's go back to the beginning.
So there's Carnus. Arcananian prophet and seer and "friend to Apollo." Only someone thinks he may be betraying his people. So one day while he's traveling to Peloponessia, they stab him repeatedly. No more Carnus, right?
Except suddenly all of their animals start dying. Livestock, fowl, horses - the pestilence is fairly merciless. So, being the superstitious lot that Greeks tended to be, they figure it's Apollo, getting revenge for his buddy Carnus. So to appease him, they make a sacrifice.
And (in typical deus ex machina fashion) the pestilence ends. So the sacrifice worked. So they decide to make it an annual event, called Carnea (named for the month they held it in, around August on today's calendar.)
And thus was born Apollo Carneus (Carneus meaning "god of the flocks"), special protector of the Dorian people. You can think of it as the Greek equivalent of "The Lamb of God", or "The Great I Am."
Little known fact: The Carnea festival is why the Spartans didn't help out Athens during the Battle of Marathon.