Tao's sword is the sword Mercenary Tao uses against Goku in their second fight.
Overview
The sword is a niuweidao (牛尾刀, "Ox Tail Saber"), a single-edged broadsword used in Chinese martial arts, although the sword's blade has a greater resemblance to the Chinese Guan Dao, Korean Hyeopdo, or Russian Sovnya.
When Tao was overpowered by Goku, he brought out a capsule. He then tossed the capsule and the sword appeared. It was used for a limited time though as Goku dodged a few attacks from Tao's blade, with Upa throwing the Power Pole to Goku, which he used to break Tao's sword. After that, they went back to regular combat.
Mercenary Tao also uses this sword in the Budokai Tenkaichi video game series. He also uses it in Dragon Ball Z: Idainaru Son Goku Densetsu, for a technique named Renshinseiryuto (連振青竜刀).