A Hasta is a type of one-handed melee long weapon similar to the two-handed spears, Hastae can be obtained either by trading with another player or using the Smithing skill upon completion of Barbarian Training on a specific barbarian anvil.
Hastae are hardly used because of the difficulty of obtaining them. Furthermore, up until recently, hastae could only be sold from player to player. They couldn't be sold on the Grand Exchange. Despite the changes, they remain very unique, somewhat rare items.