Not to confuse everyone, maybe some of the older members have a better recollection on this, but didn't the front spoiler used to be called something different. I always thought a spoiler went on the rear & the front was an air dam or some other name.
As I recall, a spoiler is a sort of wing; it "spoils" the airflow, i.e., deflects it, to create downforce. Spoilers have to be more rigid, and so are usually mounted higher on a street car.
An airdam blocks airflow under the chassis to create a vacuum under the chassis that pulls the car down (or, to be technical, that allows greater air pressure above the car to push down on it). Airdams have to be very close to the ground to be of any use, so they're usually made of some flexible material so they don't crack when they bottom out. They need side-skirts as well. A lot of ricers have the airdam/sideskirt combo.