Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with narwhals, chevrotains, musk deer, water deer, muntjac, pigs, peccaries, hippopotamuses, and walruses, or, in the case of elephants, elongated incisors. Elephants use their tusks as digging and boring tools. Elephant tusks are sexually dimorphic, being on average larger in males than in females, and entirely absent in female Asian elephants.

Source: Wikipedia