Tapion's Sword is an enchanted sword owned by Tapion during the events of the movie, Wrath of the Dragon. This blade is given to Trunks at the end of the movie, which is later used in Dragon Ball GT and Dragon Ball AF.
During the war between Hirudegarn and the Konatsians, Tapion and his young brother Minotia used their special ocarinas to hold Hirudegarn at bay. Given this opportunity, a Konatsian Wizard brandished the enchanted sword and used it to slice Hirudegarn in half.
Under Trunks' PossessionMain article: Future Trunks' sword
After Hirudegarn's defeat, Tapion gives Trunks his sword, stating that it was always meant for him; referencing to the fact that his Alternate timeline counterpart, Future Trunks, was almost always seen with his sword. It was kept by him for years as a memento of the close bond he formed with Tapion during his time on Earth.
Unlike his future counterpart, he presumably never had much use for the sword during battle, having grown up in a peaceful world.
Although the two swords might look identical, Future Trunks said that his sword was a precious memento from his master (which presumably refers to Gohan, not Tapion). Though, it has been stated in Dragon Ball: Raging Blast that Tapion did give his sword to Future Trunks. It should also be noted that at the end of the 13th Dragon Ball Z movie, the entire credit roll is accompanied by scenes of Future Trunks using his sword.