Triforce of Wisdom is a part of the sacred relic called Triforce, which appears throughout The Legend of Zelda series. It can enchance wearer's magical abilities. In Zelda: The Wand of Gamelon, Impa uses the Triforce of Wisdom to see the future or present.
In Achille12345's video, The Evil King, Impa used Triforce of Wisdom to increase Defense of the entire team. It wasn't mentioned anywhere else, but we know that Link used it in CD-I Fight Episode 2 along with Power and Courage to become Triforced Link.