Deku Shield

The Deku Shield is a simple shield made of wood in Ocarina of Time. The spiral symbol of the Kokiri appears on its surface. Link can purchase this shield in the shop in Kokiri Forest for 40 rupees or from Business Scrubs in the Lost Woods and Inside the Great Deku Tree for 50 rupees. It is highly durable in most environments, but in hot settings, its durability may be compromised by fire; it burns up if fire touches it. In such an event, Link can swap it out with the Hylian Shield just long enough to preserve it, and change it back once he gets away from flaming objects. Link needs the Deku Shield and the Kokiri Sword to convince Mido to let him see the Deku Tree for the first time.

The Deku Shield was in the beta Version of Majora's Mask. It is unknown why it was removed.

Manga
In the Ocarina of Time manga, Link carves the Deku Shield out of the Deku Tree after its death.

Trivia

 * The Deku Shield is, unsurprisingly, the shield carried into battle by Young Link in his appearance in Super Smash Bros. Melee. Perhaps the sole surprising part of this appearance is that, even if Young Link is struck by flame attacks, the Deku Shield does not burn up as it does in its sole canonical appearance.
 * The doors inside The Wind Waker's Forbidden Woods are similar to the Deku Shield, as the red symbol appears on the brown doors, forming a Deku Shield-like shape and look.