After locating the Gerudo Mesa and Cave of Ordeals in the Gerudo desert, you are able to unlock fairies and later Great Fairies at each spring around Hyrule. Smaller fairies can be bottled, restore 8 hearts when used, or when you run out of hearts. Great Fairies will give you a bottle full of Great Fairy Tears, which heal you full and temporarily boost your attack, provided you have an empty bottle and no Tears in your inventory already.

Both have an infinite supply once unlocked.

Effect - Code

Fairies in the Eldin Spring - Complete 30 rooms in the Cave of Ordeals
Fairies in the Faron Spring - Complete 20 rooms in the Cave of Ordeals
Fairies in the Lanayru Spring - Complete 40 rooms in the Cave of Ordeals
Fairies in the Ordon Spring - Complete 10 rooms in the Cave of Ordeals
Great Fairies in all springs - Complete 50 rooms in the Cave of Ordeals