ItemDex/RGBY:059

The Coin (Japanese: コイン) is an unused item or glitch item in Pokémon Red, Blue, and Yellow.

This item is stackable and with no use other than to be sold for 5 Pokédollars each. It is possible that this item was intended to be a coin from the Game Center, which in the final game cost 1000 Pokédollars for 50 coins and are stored in the Coin Case instead.