A loud sound
generally made by large, carnivorous animals
. People can't roar , or at least I've never heard them
. Although, roar can be applied to any loud, angry, violent, primal sound, as in one roared in anger
The sound of animal rage
Then again, the word 'roar' is often applied to the sound of the ocean and the noise made by a plane taking off.
I suppose pretty much any loud sound can be a roar.