The Kokiri Sword is a recurring sword in the Legend of Zelda series. Its design varies between the two games that it appears in, it is the first, shortest, and weakest sword that Link equips in both games. It is made for the small Kokiri people, so it can not be used as an adult.
The Kokiri Sword is needed along with the Deku Shield to get past Mido, who is blocking the entrance to the Great Deku Tree. The sword can be found in the Hole of Z in the Forest Training Center. Upon climbing into the Hole of Z and dodging the rolling boulder, Link finds a Treasure Chest containing the Kokiri Sword. When found, the description states that Link is only borrowing the sword, but Link ends up keeping it forever. When Link is an adult he can not use it, for he is much too large for it.
The Kokiri Sword is the sword that Link has in the beginning of the game. It is the same sword as in the last game, but has a different design for some unknown reason. The sword can later be forged into the Razor Sword by Zubora and Gabora, but it goes back to the regular Kokiri Sword after 100 slashes. It can also be permanently re-forged into the Gilded Sword, which is three times as powerful as the Kokiri Sword.
In the Majora's Mask DLC, Young Link uses it as his weapon