Is an elephant considered as a prey or predator?

Yes elephants use their tusks to fight against predators.

ADDENDUM:

Elephants have a variety of defense mechanisms. Because they are highly intelligent, they know that the best defense is a good offense, and they will go on the attack.

Their huge size alone is a deterrent and combined with their weight, both can be used as formidable weapons. They kick and strike with their feet; one blow can easily kill a predator. They also will crush an enemy to death by kneeling on it or stepping on it with a foot.

Elephants have used their long trunks for weapons and are deadly accurate with them. One strike can completely disable a predator.

If a lion or lions has managed to get on the back of an elephant, elephants will whirl and create a centrifugal force that dislodges the predator from their back and, if close to water, will use water both to prevent attacks from the rear or to retreat into.

When you add tusks into the equation, only the most daring of the largest predators, with sufficient numbers, would undertake such a dangerous feat.