The Reload Card is the card used by Sora, Riku, and all non-Heartless bosses in Kingdom Hearts: Chain of Memories and Kingdom Hearts Re:Chain of Memories. It is a black colored card with no picture, but instead a large number in the middle of it.
This card reloads all reloadable cards in the deck. Each time it is used, it takes a longer amount of time for the cards to be reloaded. One reload used leads to the next tier (two second reload). Two reloads leads to the tier after that (3 second reload). The tiers stop there, and all reloads after that in the given battle take 3 seconds, unless a card is used to reset the reload counter.
The large number on the card shows how long it needs to charge, with 1 being one second, 2 being two seconds, and 3 being three seconds. The maximum number is 3. The reload time can be reset with an Elixir or certain Enemy Cards.
The Reload Card Riku uses has no number, and a simple push of the button will reload his cards instantly. The reason why Sora's Reload Card takes time and Riku's doesn't is currently a mystery, although the no-reload factor plays a fairly largely sized role in Riku's battles, as he is heavily melee oriented, lacking magic cards in favor of a few powerful sleights and many attack cards.
In Kingdom Hearts Re:Chain of Memories, Marluxia's Angelic form has a sleight that scatters every card in Sora's deck, including the Reload Card. Sora must get the Reload card (it can be found by its grey back and black front) to reload his cards again. If Sora does not retrieve his reload card, the effect can be devastating, as he can no longer reload his deck.