Glaive throwers are ballista type weapons that throw glaives (a three bladed disk) at enemy forces. Generally used by members of the various elven races, they have been handy at fighting enemy forces of the night elves, blood elves, and even alliance.
Glaive Thrower (blood elves)
The blood elf glaive thrower' helped the Blood Elves try to stop Arthas as he was trying to activate the Icecrown Obelisks to free the Lich King from the Frozen Throne in Warcraft III. It is a siege unit that has a long range, built in the Blood Elven Barracks. The Blood Elves Glaive Throwers are an upgrade to the High Elves ballistas.
Glaive Thrower (night elves)
Night elves also upgraded their Ballistae into glaive throwers as well. They continue to use them to this day.
Glaive Throwers in World of Warcraft
Glaive throwers and their ammo are scattered all over the World of Warcraft. They are often found on Kalimdor and can be seen in such places as Ashenvale, as well as Silithus.