The Triforce is a sacred item that appears throughout The Legend of Zelda. It is split into three different parts: the Triforce of Courage (associated with Link), the Triforce of Wisdom (associated with Zelda), and the Triforce of Power (associated with Ganondorf). The Triforce does not distinguish between "good" and "evil," and when the three pieces of the Triforce are reunited, it can grant whatever wish the holder desires. In the Zelda series, Ganon seeks the Triforce in order to gain power and take over Hyrule while Link and Zelda attempt to stop him.
In the Super Smash Bros. series
The Triforce appears as the symbol of The Legend of Zelda series in all five Smash Bros. games. In the opening movie of Super Smash Bros. Melee, Link's, Zelda's, and Ganondorf's arms appear, with each of them wielding their respective piece of the Triforce. It also appears as structures on Zelda and Sheik's Target Test stages, and in the Underground Maze of Melee's Adventure Mode as a goal one must reach to complete the stage. In Super Smash Bros. Brawl, Super Smash Bros. 4, and Super Smash Bros. Ultimate, the Triforce is seen in Link, Toon Link, and Young Link's Final Smash, Triforce Slash, as it traps the opponent while Link, Toon Link, or Young Link slashes them. In Super Smash Bros. Ultimate, Zelda uses the Triforce of Wisdom in her new Final Smash, where she traps the opponents in the titular piece of the Triforce. Additionally, the Animal Crossing Triforce amusingly appears as one of the various items thrown into the house as it's being built in Dream Home.