A roar was a vocalization made by certain animals and lifeforms such as the El-Adrel IV entity. (TNG: "Darmok") Some animals, such as grishnar cats, used the sound to evoke fear as an act of self-defense. (DS9: "The Way of the Warrior")
The collective loud sound of a crowd of people was sometimes called a roar (TOS: "Day of the Dove"), as was the sound of thunder. (DS9: "The Ascent")
Female Klingons roared when seeking a mate. (TNG: "The Dauphin")
Edosians were also able to roar when angered. (LD: "Much Ado About Boimler")