Genprey Fangs are fangs obtained in all 1st Generation and 2nd Generation Monster Hunter games from Genprey and Gendrome although in some cases they can be purchased. They are used as crafting materials to make some Paralyze attribute weapons such as the Deasthprize sword line.
Another common use of Genprey Fangs is in combiniations, as they are one of two components used to make the Shock Trap, an item regularly used by Hunters. the other component in this combination is a Trap Tool.
In your pack, and in your chest, up to 99 Genprey Fangs can occupy a single slot before having to move on to a new one.