It's number of forks branching off from the main 2 antlers. The exact decription is -
if(player.horns > 0)
outputText(" Two antlers, forking into " + num2Text(player.horns) + " points, have sprouted from the top of your head, forming a spiky, regal crown of bone.");
So 6 points would be -
Two antlers, forking into six points, have sprouted from the top of your head, forming a spiky, regal crown of bone.