Deku Seed

Slingshot Pellets are items, usually seeds, that are used as ammunition in a slingshot. The ammunition is different depending on the slingshot used.

Deku Seeds
Deku Seeds are found in Ocarina of Time. They are common items, especially inside the Great Deku Tree. These seeds are used as ammunition for the Fairy Slingshot. The Deku Seeds can only be used as a Child due to the Fairy Slingshot not having any use as an adult. They are held in the Deku Seed Bag, which can be upgraded to hold 40 or 50 seeds.

On another note, the enemy Skull Kid shoots Deku Seeds from his flute. These aren't particularly strong, but they are shot fast.

Mystical Seeds
Mystical Seeds are a type of ammunition for the Slingshot or Seed Shooter introduced in Oracle of Ages and Oracle of Seasons. There are five types: Ember, Scent, Pegasus, Gale, and Mystery.

Pumpkin Seeds
Pumpkin Seeds are a type of Slingshot ammunition introduced in Twilight Princess. Sera in Ordon Village sells these seeds in her shop along with the slingshot, but never again after the slingshot is bought. They are one of the possible foods Ordonians eat. Oddly, Pumpkin Seeds do not always appear when Link smashes a pumpkin; in fact, the majority of the pumpkins don't have seeds in them. Pumpkin Seeds automatically load into Link's slingshot upon obtaining them. Deku Seeds can also still be used as ammunition.