Anlers are true bone, composed of calcium and phosphorus. But, unlike most mammal bones, they are solid and without marrow. Both horns and antlers are actually extended growths of the frontal skull plate. Horns have a porous core and the outer surface is composed of keratin, the same substance as fingernails.

Taken from : The Deer of North America by Leonard Lee Rue III.

I call them horns on occasion. Its just slang.